CMerkleBlock::CMerkleBlock called IsRelevantAndUpdate() on each transaction
in order, which (due to the outpoint-adding feature) assumes a topological
order of transactions in order to work correctly. If an outpoint of interest were
created later in a block than when gets spent, then it would be added into
the bloom filter too late, and thus that spending transaction would get missed.
This changes CMerkleBlock::CMerkleBlock to scan all outputs first, then
make a second loop to scan all inputs. This requires breaking up the
IsRelevantAndUpdate() function into two parts. The original
IsRelevantAndUpdate() functionality remains fully intact however, as it
gets called from mempool-related code (mempool has topological order)
and tests.
Note that vMatchedTxn.push_back is moved into the second loop so that
index i keeps ascending order, in case that is somehow relevant.
A two-loop construction like this will very slightly increase the false
positive rate.