This changes the database access APIs and each of the "manager"
packages (waddrmgr/wstakemgr) so that transactions are opened (only)
by the wallet package and the namespace buckets that each manager
expects to operate on are passed in as parameters.
This helps improve the atomicity situation as it means that many
calls to these APIs can be grouped together into a single
database transaction.
This change does not attempt to completely fix the "half-processed"
block problem. Mined transactions are still added to the wallet
database under their own database transaction as this is how they are
notified by the consensus JSON-RPC server (as loose transactions,
without the rest of the block that contains them). It will make
updating to a fixed notification model significantly easier, as the
same "manager" APIs can still be used, but grouped into a single
atomic transaction.
In https://github.com/btcsuite/btcwallet/pull/419#issuecomment-212482492
I mentioned that btcwallet should wait until btcd also switches back
to upstream package paths so that duplicate packages are not included
in and bloat the btcwallet binary. Even while btcd has not yet
switched to the upstream flags package, this change can still be made
now since it is only used by btcd's main package, which is not
included in btcwallet.
