This commit updates the calls into btcutil and btcwire for the latest API
changes which remove the need for the protocol version for serialization
and deserialization of blocks and transactions.
Fix error returns in InsertBlock and FetchBlockBySha
Give up on return by name in InsertBlock() and return explicit
err one location in FetchBlockBySha to return proper error value
The Db interface is intended to work with block heights as opposed to
specific database ids which may or may not be the same as the block
height. This commits changes the function names to make that distinction
a little more clear.
