Simplify Tx.check slightly.
Simplify Tx.check slightly.

shivaenigma/pycoin,richardkiss/pycoin,richardkiss/pycoin,pycoin/pycoin,zsulocal/pycoin,mperklin/pycoin,zsulocal/pycoin,pycoin/pycoin,XertroV/pycoin,mperklin/pycoin,XertroV/pycoin,shivaenigma/pycoin