Transaction: data driven tests
Transaction: add sequence parameter to addInput
Transaction: re-adds getHash as a pure hash
Transaction: add hash as addInput parameter
Transaction: remove untestable assert

Also changes the fromBuffer sanity test to use a clearer message that is
taken from the fixtures.
Transaction: move constants to Transaction
Transaction: improve hash length checking + tests
Merge pull request #214 from dcousens/txtests

Transaction tests