Continue analysis after parse errors

[JukkaL]

As continuation of #966, mypy should continue processing additional modules even if there is a parse error in one module. Currently mypy stops at a parse error.

Any module that can't be parsed should be considered to be the equivalent of having type Any elsewhere in the program.

[JukkaL]

As the parser is now in better shape this is no longer as urgent as this used to be.

[hauntsaninja]

While blocking errors are a bad experience, they're fairly rare these days