fake blockchain generator + some simple performance test
network :no_difficulty option to avoid monkey patching
refactor FakeBlockchain to work around caching issue
fix fake chain generation

genesis block was not being yield, so the blocki #1 was becoming genesis

* moved parsing blocks from disk away from the benchmark
* added check to make sure block was really stored in the main chain
check for already spent outputs with a single query during block validation

+ add index on txin (prev_out, prev_out_index)
don't log "relaying block ..." before deciding if the block is relayed
Merge remote-tracking branch 'comboy/validation_optimizations2'
use storage config instead of asking to build tx.nhash index during migrations
Merge remote-tracking branch 'refs/remotes/comboy/fake_chain'