Automatically add any matching outputs to a filter during matching.
Add a CBlock.GetBlockHeader
Add a CMerkleBlock to store merkle branches of filtered txes.
Add test cases for CMerkleBlock and CBloomFilter.
Relay CMerkleBlocks when asked for MSG_FILTERED_BLOCK
Let a node opt out of tx invs before we get a their bloom filter

Note that the default value for fRelayTxes is false, meaning we
now no longer relay tx inv messages before receiving the remote
peer's version message.
Add a nTweak to bloom filters to tweak the seed.
Add CPartialMerkleTree

This adds a compact representation for a subset of a merkle tree's
nodes.
Use CPartialMerkleTree for CMerkleBlock transactions.