d1c3762 Revert "Revert "Enable policy enforcing GetMedianTimePast as the end point of lock-time constraints"" (Gregory Maxwell)
e4e5334 Restore MedianTimePast for locktime. (Gregory Maxwell)
Previously, the undo weren't being flushed during a reindex because
fKnown was set to true in FindBlockPos. That is the correct behaviour
for block files as they aren't being touched, but undo files are
touched.
This changes the behaviour to always flush when switching to a new file
(even for block files, though that isn't really necessary).
The docs talk about bits 2 and 4 instead of 2 and 3, and bits are being
indexed from both 1 (describing nCode) and 0 (in second example).
Changed to use zero-indexing for all.
6342a48 Init: Use DEFAULT_TRANSACTION_MINFEE in help message (MarcoFalke)
a9c73a1 [wallet] Add comments for doxygen (MarcoFalke)
6b0e622 [wallet] Refactor to use new MIN_CHANGE (MarcoFalke)
a6efc01 Bugfix: Omit wallet-related options from -help when wallet is disabled (Luke Dashjr)
5f9260f Bugfix: If genproclimit is omitted to RPC setgenerate, don't change it; also show correct default in getmininginfo (Luke Dashjr)
420a82f Bugfix: Describe dblogsize option correctly (it refers to the wallet database, not memory pool) (Luke Dashjr)
caa3d42 Bugfix: RPC: blockchain: Display correct defaults in help for verifychain method (Luke Dashjr)
Moves the call Initialize() from init.cpp to CreateWithArguments() and handles the
return value. Moves the call Shutdown() from init.cpp to destructor.
Changes Initialize() and Shutdown() to protected members.
Revert "Revert "Add rules--presently disabled--for using GetMedianTimePast as endpoint for lock-time calculations""
This reverts commit 40cd32e835.
After careful analysis it was determined that the change was, in fact, safe and several people were suffering
momentary confusion about locktime semantics.
When processing a new transaction, in addition to spending the Coins of its txin's it creates a new Coins for its outputs. The existing ModifyCoins function will first make sure this Coins does not already exist. It can not exist due to BIP 30, but because of that the lookup can't be cached and always has to go to the database. Since we are creating the coins to match the new tx anyway, there is no point in checking if they exist first anyway. However this should not be used for coinbase tx's in order to preserve the historical behavior of overwriting the two existing duplicate tx pairs.
40cd32e Revert "Add rules--presently disabled--for using GetMedianTimePast as endpoint for lock-time calculations" (Gregory Maxwell)
8537ecd Revert "Enable policy enforcing GetMedianTimePast as the end point of lock-time constraints" (Gregory Maxwell)
This reverts commit 9d55050773.
As noted by Luke-Jr, under some conditions this will accept transactions which are invalid by the network
rules. This happens when the current block time is head of the median time past and a transaction's
locktime is in the middle.
This could be addressed by changing the rule to MAX(this_block_time, MTP+offset) but this solution and
the particular offset used deserve some consideration.
* Introduce new constant MIN_CHANGE and use it instead of the
hardcoded "CENT"
* Add test case for MIN_CHANGE
* Introduce new constant for -mintxfee default:
DEFAULT_TRANSACTION_MINFEE = 1000
Reduce the default limits on maximum number of transactions and the cumulative size of those transactions in both ancestor and descendant packages to 25 txs and 101kb total size.
Update the unittest that is meant to catch a transaction that is invalid
because it has a null input. The old test failed not because of that
but because it was considered a coinbase with too large script. This is
already checked with a different test, though.
The new test is *not* a coinbase since it has two inputs, but one of
them is null. This really checks the corresponding code path in
CheckTransaction.
143d173 Use BOOST_CHECK_MESSAGE() rather than BOOST_CHECK() in alerts_tests.cpp and initialize strMiscWarning before calling PartitionCheck()." (Eric Lombrozo)
* -maxuploadtarget can be set in MiB
* if <limit> - ( time-left-in-24h-cycle / 600 * MAX_BLOCK_SIZE ) has reach, stop serve blocks older than one week and filtered blocks
* no action if limit has reached, no guarantee that the target will not be surpassed
* add outbound limit informations to rpc getnettotals
dea8d21 Enable policy enforcing GetMedianTimePast as the end point of lock-time constraints (Mark Friedenbach)
9d55050 Add rules--presently disabled--for using GetMedianTimePast as endpoint for lock-time calculations (Mark Friedenbach)
Until now there were quite a few leftovers, and only the coverage
related files in `src/` were cleaned, while the ones in the other dirs
remained. `qa/tmp/` is related to the BitcoinJ tests, and `cache/` is
related to RPC tests.
Transactions are not allowed in the memory pool or selected for inclusion in a block until their lock times exceed chainActive.Tip()->GetMedianTimePast(). However blocks including transactions which are only mature under the old rules are still accepted; this is *not* the soft-fork required to actually rely on the new constraint in production.
The lock-time code currently uses CBlock::nTime as the cutoff point for time based locked transactions. This has the unfortunate outcome of creating a perverse incentive for miners to lie about the time of a block in order to collect more fees by including transactions that by wall clock determination have not yet matured. By using CBlockIndex::GetMedianTimePast from the prior block instead, the self-interested miner no longer gains from generating blocks with fraudulent timestamps. Users can compensate for this change by simply adding an hour (3600 seconds) to their time-based lock times.
If enforced, this would be a soft-fork change. This commit only adds the functionality on an unexecuted code path, without changing the behaviour of Bitcoin Core.
Nagle appears to be a significant contributor to latency now that the static
sleeps are gone. Most of our messages are relatively large compared to
IP + TCP so I do not expect this to create enormous overhead.
This may also reduce traffic burstyness somewhat.
Add a comment that explains why the initial "getheader" requests are
made starting from the block preceding the currently best one.
Thanks to sdaftuar for the explanation!
There is no exact science to setting this parameter, but 5000
(just over 1 US cent at the time of writing) is higher than the
cost to relay a transaction around the network (the new benchmark
due to mempool limiting).
After each transaction which is added to mempool, we first call
Expire() to remove old transactions, then throwing away the
lowest-feerate transactions.
After throwing away transactions by feerate, we set the minimum
relay fee to the maximum fee transaction-and-dependant-set we
removed, plus the default minimum relay fee.
After the next block is received, the minimum relay fee is allowed
to decrease exponentially. Its halflife defaults to 12 hours, but
is decreased to 6 hours if the mempool is smaller than half its
maximum size, and 3 hours if the mempool is smaller than a quarter
its maximum size.
The minimum -maxmempool size is 40*-limitdescendantsize, as it is
easy for an attacker to play games with the cheapest
-limitdescendantsize transactions. -maxmempool defaults to 300MB.
This disables high-priority transaction relay when the min relay
fee adjustment is >0 (ie when the mempool is full). When the relay
fee adjustment drops below the default minimum relay fee / 2 it is
set to 0 (re-enabling priority-based free relay).
(note the 9x multiplier on (void*)'s for CTxMemPool::DynamicMemoryUsage
was accidentally introduced in 5add7a7 but should have waited for this
commit which adds the extra index)
To bridge the time until a dynamic method for determining this fee is
merged.
This is especially aimed at the stable releases (0.10, 0.11) because
full mempool limiting, as will be in 0.12, is too invasive and risky to
backport.
1534d9a Creates unittests for addrman, makes addrman testable. Adds several unittests for addrman to verify it works as expected. Makes small modifications to addrman to allow deterministic and targeted tests. (EthanHeilman)
Adds an `obfuscate` parameter to `CLevelDBWrapper` and makes use of it
for all new chainstate stores built via `CCoinsViewDB`. Also adds an
`Xor` method to `CDataStream`.
Thanks to @sipa @laanwj @pstratem @dexX7 @KyrosKrane @gmaxwell.
This adds SCRIPT_VERIFY_LOW_S to STANDARD_SCRIPT_VERIFY_FLAGS which
will make the node require the canonical 'low-s' encoding for
ECDSA signatures when relaying or mining.
Consensus behavior is unchanged.
The rational is explained in a81cd96805:
Absent this kind of test ECDSA is not a strong signature as given
a valid signature {r, s} both that value and {r, -s mod n} are valid.
These two encodings have different hashes allowing third parties a
vector to change users txids. These attacks are avoided by picking
a particular form as canonical and rejecting the other form(s); in
the of the LOW_S rule, the smaller of the two possible S values is
used.
If widely deployed this change would eliminate the last remaining
known vector for nuisance malleability on boring SIGHASH_ALL
p2pkh transactions. On the down-side it will block most
transactions made by sufficiently out of date software.
Unlike the other avenues to change txids on boring transactions this
one was randomly violated by all deployed bitcoin software prior to
its discovery. So, while other malleability vectors where made
non-standard as soon as they were discovered, this one has remained
permitted. Even BIP62 did not propose applying this rule to
old version transactions, but conforming implementations have become
much more common since BIP62 was initially written.
Bitcoin Core has produced compatible signatures since a28fb70e in
September 2013, but this didn't make it into a release until 0.9
in March 2014; Bitcoinj has done so for a similar span of time.
Bitcoinjs and electrum have been more recently updated.
This does not replace the need for BIP62 or similar, as miners can
still cooperate to break transactions. Nor does it replace the
need for wallet software to handle malleability sanely[1]. This
only eliminates the cheap and irritating DOS attack.
[1] On the Malleability of Bitcoin Transactions
Marcin Andrychowicz, Stefan Dziembowski, Daniel Malinowski, Łukasz Mazurek
http://fc15.ifca.ai/preproceedings/bitcoin/paper_9.pdf
Previously only one PUSHDATA was allowed, needlessly limiting
applications such as matching OP_RETURN contents with bloom filters that
operate on a per-PUSHDATA level. Now any combination that passes
IsPushOnly() is allowed, so long as the total size of the scriptPubKey
is less than 42 bytes. (unchanged modulo non-minimal PUSHDATA encodings)
Also, this fixes the odd bug where previously the PUSHDATA could be
replaced by any single opcode, even sigops consuming opcodes such as
CHECKMULTISIG. (20 sigops!)
Previously unlike other transaction types the TX_SCRIPTHASH would not
clear vSolutionsRet, which means that unlike other transaction types if
it was called twice in a row you would get the result of the previous
invocation as well.
Avoid calling gettimeofday every time through the benchmarking loop, by keeping
track of how long each loop takes and doubling the number of iterations done
between time checks when they take less than 1/16'th of the total elapsed time.
Benchmarking framework, loosely based on google's micro-benchmarking
library (https://github.com/google/benchmark)
Wny not use the Google Benchmark framework? Because adding Even More Dependencies
isn't worth it. If we get a dozen or three benchmarks and need nanosecond-accurate
timings of threaded code then switching to the full-blown Google Benchmark library
should be considered.
The benchmark framework is hard-coded to run each benchmark for one wall-clock second,
and then spits out .csv-format timing information to stdout. It is left as an
exercise for later (or maybe never) to add command-line arguments to specify which
benchmark(s) to run, how long to run them for, how to format results, etc etc etc.
Again, see the Google Benchmark framework for where that might end up.
See src/bench/MilliSleep.cpp for a sanity-test benchmark that just benchmarks
'sleep 100 milliseconds.'
To compile and run benchmarks:
cd src; make bench
Sample output:
Benchmark,count,min,max,average
Sleep100ms,10,0.101854,0.105059,0.103881
This makes sure that the event loop eventually terminates, even if an
event (like an open timeout, or a hanging connection) happens to be
holding it up.
Add a WaitExit() call to http's WorkQueue to make it delete the work
queue only when all worker threads stopped.
This fixes a problem that was reproducable by pressing Ctrl-C during
AppInit2:
```
/usr/include/boost/thread/pthread/condition_variable_fwd.hpp:81: boost::condition_variable::~condition_variable(): Assertion `!ret' failed.
/usr/include/boost/thread/pthread/mutex.hpp:108: boost::mutex::~mutex(): Assertion `!posix::pthread_mutex_destroy(&m)' failed.
```
I was assuming that `threadGroup->join_all();` would always have been
called when entering the Shutdown(). However this is not the case in
bitcoind's AppInit2-non-zero-exit case "was left out intentionally
here".
Shutting down the HTTP server currently breaks off all current requests.
This can create a race condition with RPC `stop` command, where the calling
process never receives confirmation.
This change removes the listening sockets on shutdown so that no new
requests can come in, but no longer breaks off requests in progress.
Meant to fix#6717.
The "please check your computer's data and time" message when the clock
deviates from the network currently generates an overkill of messages:
orion@lethe:~/bitcoin$ src/bitcoind
Warning: Warning: Please check that your computer's date and time are correct! If your clock is wrong Bitcoin Core will not work properly.
In the log:
2015-09-27 16:24:13 *** Warning: Please check that your computer's date and time are correct! If your clock is wrong Bitcoin Core will not work properly.
2015-09-27 16:24:13 Warning: Warning: Please check that your computer's date and time are correct! If your clock is wrong Bitcoin Core will not work properly.
Remove one level of 'Warning:' and reduce to one log message.
af3208b Resolve issue 3166. These changes decode valid SIGHASH types on signatures in assembly (asm) representations of scriptSig scripts. This squashed commit incorporates substantial helpful feedback from jtimon, laanwj, and sipa. (mruddy)
CalculateMemPoolAncestors was always looping over a transaction's inputs
to find in-mempool parents. When adding a new transaction, this is the
correct behavior, but when removing a transaction, we want to use the
ancestor set that would be calculated by walking mapLinks (which should
in general be the same set, except during a reorg when the mempool is
in an inconsistent state, and the mapLinks-based calculation would be the
correct one).
* Raise the debug window when hidden behind other windows
* Switch to the debug window when on another virtual desktop
* Show the debug window when minimized
This change is a conceptual copy of 5ffaaba and 382e9e2
Assume that when a wallet transaction has a valid block hash and transaction position
in it, the transaction is actually there. We're already trusting wallet data in a
much more fundamental way anyway.
To prevent backward compatibility issues, a new record is used for storing the
block locator in the wallet. Old wallets will see a wallet file synchronized up
to the genesis block, and rescan automatically.
7aac6db [QT] dump banlist to disk in case of ban/unban over QT (Jonas Schnelli)
7f90ea7 [QA] adabt QT_NO_KEYWORDS for QT ban implementation (Jonas Schnelli)
07f70b2 [QA] fix netbase tests because of new CSubNet::ToString() output (Jonas Schnelli)
4ed0510 [Qt] call DumpBanlist() when baning unbaning nodes (Philip Kaufmann)
be89292 [Qt] reenabling hotkeys for ban context menu, use different words (Jonas Schnelli)
b1189cf [Qt] adapt QT ban option to banlist.dat changes (Jonas Schnelli)
65abe91 [Qt] add sorting for bantable (Philip Kaufmann)
51654de [Qt] bantable polish (Philip Kaufmann)
cdd72cd [Qt] simplify ban list signal handling (Philip Kaufmann)
43c1f5b [Qt] remove unused timer-code from banlistmodel.cpp (Jonas Schnelli)
e2b8028 net: Fix CIDR notation in ToString() (Wladimir J. van der Laan)
9e521c1 [Qt] polish ban table (Philip Kaufmann)
607809f net: use CIDR notation in CSubNet::ToString() (Jonas Schnelli)
53caec6 [Qt] bantable overhaul (Jonas Schnelli)
f0bcbc4 [Qt] bantable fix timestamp 64bit issue (Jonas Schnelli)
6135309 [Qt] banlist, UI optimizing and better signal handling (Jonas Schnelli)
770ca79 [Qt] add context menu with unban option to ban table (Jonas Schnelli)
5f42132 [Qt] add ui signal for banlist changes (Jonas Schnelli)
ad204df [Qt] add banlist table below peers table (Jonas Schnelli)
50f0908 [Qt] add ban functions to peers window (Jonas Schnelli)
ddf98d1 Make RPC tests cope with server-side timeout between requests (Wladimir J. van der Laan)
2190ea6 rpc: Split option -rpctimeout into -rpcservertimeout and -rpcclienttimeout (Wladimir J. van der Laan)
8b2d6ed http: Disable libevent debug logging, if not explicitly enabled (Wladimir J. van der Laan)
5ce43da init: Ignore SIGPIPE (Wladimir J. van der Laan)
The two timeouts for the server and client, are essentially different:
- In the case of the server it should be a lower value to avoid clients
clogging up connection slots
- In the case of the client it should be a high value to accomedate slow
responses from the server, for example for slow queries or when the
lock is contended
Split the options into `-rpcservertimeout` and `-rpcclienttimeout` with
respective defaults of 30 and 900.
Associate with each CTxMemPoolEntry all the size/fees of descendant
mempool transactions. Sort mempool by max(feerate of entry, feerate
of descendants). Update statistics on-the-fly as transactions enter
or leave the mempool.
Also add ancestor and descendant limiting, so that transactions can
be rejected if the number or size of unconfirmed ancestors exceeds
a target, or if adding a transaction would cause some other mempool
entry to have too many (or too large) a set of unconfirmed in-
mempool descendants.
Ignore SIGPIPE on all non-win32 OSes, otherwise an unexpectedly disconnecting
RPC client will terminate the application. This problem was introduced
with the libhttp-based RPC server.
Fixes#6660.
The thin space QT html hack results in cut-off chars/nums after a line break.
Avoid word wrap line breaks by using a smaller font and a line break before each alternative value)
GetTransaction needs to lock cs_main until ReadBlockFromDisk completes, the data inside CBlockIndex's can change since pruning. This lock was held by all calls to GetTransaction except rest_tx.
- removes mapBlockIndex find operation
- theoretically allows removing the cs_main lock during zqm notification while introducing a new file position lock
- add missing NULL pointer checks
- add better comments and reorder some code in rpcconsole.cpp
- remove unneeded leftovers in bantable.cpp
- update bantable column sizes to prevent cutting of banned until
- remove banListChanged signal from client model
- directly call clientModel->getBanTableModel()->refresh() without the way
over clientModel->updateBanlist()
- also fix clearing peer detail window, when selecting (clicking)
peers in the ban list
Continues Johnathan Corgan's work.
Publishing multipart messages
Bugfix: Add missing zmq header includes
Bugfix: Adjust build system to link ZeroMQ code for Qt binaries
We log the cleanSubVer as part of connect. It is not uniquely more informative
than any of the other data we have about a peer, often less. It's also often
long now as well. There is no need to output it as part of mempoolrej,
AcceptToMemoryPool, or pong entries. Leaving it out makes our log entries
more uniform and consistent.
This patch changes the way the suffix (giving the requested data format) is
parsed for REST requests. Before, the string was split at '.'
characters and it was assumed that the second part was the suffix.
Now, we look for the last dot and use that to determine the suffix.
This allows for strings that contain dots (not used now, though), and
seems, in general, to be clearer and more intuitive.
Complete rescan is incompatible with pruning, but rescan is optional on
our wallet key import RPCs. Import on use is very useful in some common
situations in conjunction with pruning, e.g. merchant payment tracking.
This reenables importprivkey/importaddress/importpubkey when rescan
is not used.
In the future we should consider changing the rescan argument to allow depth
or date to allow limited rescanning when compatible with the retained
block depth.
Lets nodes advertise that they offer bloom filter support explicitly.
The protocol version bump allows SPV nodes to assume that NODE_BLOOM is
set if NODE_NETWORK is set for pre-70011 nodes.
Also adds an option to turn bloom filter support off for nodes which
advertise a version number >= 70011. Nodes attempting to use bloom
filters on such protocol versions are banned, and a later upgade
should drop nodes of an older version which attempt to use bloom
filters.
Much code stolen from Peter Todd.
Implements BIP 111
`nMinPingUsecTime` was left uninitialized in CNode.
The correct initialization for a minimum-until-now is int64_t's max value, so initialize it to that.
Thanks @MarcoFalke for noticing.
d528025 Revert "rpc-tests: re-enable rpc-tests for Windows" (Wladimir J. van der Laan)
1e700c9 doc: update deps in build-unix.md after libevent (Wladimir J. van der Laan)
26c9b83 Move windows socket init to utility function (Wladimir J. van der Laan)
4be0b08 libevent: Windows reuseaddr workaround in depends (Cory Fields)
3a174cd Fix race condition between starting HTTP server thread and setting EventBase() (Wladimir J. van der Laan)
6d2bc22 Document options for new HTTP/RPC server in --help (Wladimir J. van der Laan)
be33f3f Implement RPCTimerHandler for Qt RPC console (Wladimir J. van der Laan)
57d85d9 doc: mention SSL support dropped for RPC in release notes (Wladimir J. van der Laan)
40b556d evhttpd implementation (Wladimir J. van der Laan)
ee2a42b tests: GET requests cannot have request body, use POST in rest.py (Wladimir J. van der Laan)
6e996d3 tests: fix qt payment test (Cory Fields)
3140ef9 build: build-system changes for libevent (Wladimir J. van der Laan)
a9af234 libevent: add depends (Cory Fields)
6a21dd5 Remove rpc_boostasiotocnetaddr test (Wladimir J. van der Laan)
8f9301c qa: Remove -rpckeepalive tests from httpbasics (Wladimir J. van der Laan)
51fcfc0 doc: remove documentation for rpcssl (Wladimir J. van der Laan)
The main effect is to exit processing for recently-rejected hashes,
in case they are pushed to us without prior advertisement. This
behavior was seen in the wild.
An additional effect is to do early checks for mempool or mapOrphan
existence. No logging or nDoS tracking is needed for failures of
these checks.
027de94 Use network group instead of CNetAddr in final pass to select node to disconnect (Patrick Strateman)
000c18a Fix comment (Patrick Strateman)
fed3094 Acquire cs_vNodes before changing refrence counts (Patrick Strateman)
69ee1aa CNodeRef copy constructor and assignment operator (Patrick Strateman)
dc81dd0 Return false early if vEvictionCandidates is empty (Patrick Strateman)
17f3533 Better support for nodes with non-standard nMaxConnections (Patrick Strateman)
1317cd1 RAII wrapper for CNode* (Patrick Strateman)
df23937 Add comments to AttemptToEvictConnection (Patrick Strateman)
a8f6e45 Remove redundant whiteconnections option (Patrick Strateman)
b105ba3 Prefer to disconnect peers in favor of whitelisted peers (Patrick Strateman)
2c70153 AttemptToEvictConnection (Patrick Strateman)
4bac601 Record nMinPingUsecTime (Patrick Strateman)
ae037b7 Refactor: Move failure conditions to the top of AcceptConnection (Patrick Strateman)
1ef4817 Refactor: Bail early in AcceptConnection (Patrick Strateman)
541a1dd Refactor: AcceptConnection (Patrick Strateman)
Split StartHTTPServer into InitHTTPServer and StartHTTPServer to give
clients a window to register their handlers without race conditions.
Thanks @ajweiss for figuring this out.
Implement RPCTimerHandler for Qt RPC console, so that `walletpassphrase`
works with GUI and `-server=0`.
Also simplify HTTPEvent-related code by using boost::function directly.
- *Replace usage of boost::asio with [libevent2](http://libevent.org/)*.
boost::asio is not part of C++11, so unlike other boost there is no
forwards-compatibility reason to stick with it. Together with #4738 (convert
json_spirit to UniValue), this rids Bitcoin Core of the worst offenders with
regard to compile-time slowness.
- *Replace spit-and-duct-tape http server with evhttp*. Front-end http handling
is handled by libevent, a work queue (with configurable depth and parallelism)
is used to handle application requests.
- *Wrap HTTP request in C++ class*; this makes the application code mostly
HTTP-server-neutral
- *Refactor RPC to move all http-specific code to a separate file*.
Theoreticaly this can allow building without HTTP server but with another RPC
backend, e.g. Qt's debug console (currently not implemented) or future RPC
mechanisms people may want to use.
- *HTTP dispatch mechanism*; services (e.g., RPC, REST) register which URL
paths they want to handle.
By using a proven, high-performance asynchronous networking library (also used
by Tor) and HTTP server, problems such as #5674, #5655, #344 should be avoided.
What works? bitcoind, bitcoin-cli, bitcoin-qt. Unit tests and RPC/REST tests
pass. The aim for now is everything but SSL support.
Configuration options:
- `-rpcthreads`: repurposed as "number of work handler threads". Still
defaults to 4.
- `-rpcworkqueue`: maximum depth of work queue. When this is reached, new
requests will return a 500 Internal Error.
- `-rpctimeout`: inactivity time, in seconds, after which to disconnect a
client.
- `-debug=http`: low-level http activity logging
When running the rpc tests in Wine, nodes often fail to listen on localhost
due to a stale socket from a previous run. This aligns the behavior with other
platforms.
Fix https://github.com/bitcoin/bitcoin/issues/6558. In particular, stop
parsing JSON after the first object or array is finished. Check that no
other garbage follows, and fail the parser if it does.
c5c1edf Fix spelling mistake in -> if. (Mark Friedenbach)
e846b2a Correct a possibly intentional pun that is nevertheless hard to read: "two times of nLockTime." What is meant is that there are two kinds, or categories of nLockTime. (Mark Friedenbach)
Since the introduction of the ScriptForMining callback, the mining
functions (setgenerate and generate) crash with an assertion failure
(due to a NULL pointer script returned) if the keypool is empty. Fix
this by giving a proper error.
