Possibility to replace source and obtain ContractDefinition by name.
Merge pull request #649 from chriseth/sol_replaceSources

Possibility to replace source and obtain ContractDefinition by name.
Update serpent.
Merge branch 'develop' of github.com:ethereum/cpp-ethereum into develop
Merge branch 'develop' into poc-7+
Additional serpent files.
Merge branch 'develop' into poc-7+