delegate calls to other methods on socket

So, here's my new, updated, more general solution to the same issue as gabrielfalcao/HTTPretty#50. It uses getattr to delegate all unknown calls to the fake socket through to the underlying socket implementation, rather than specifically defining delegators for specific methods.

A word of warning though - I couldn't write tests for this without mocks, and so used 'mock' in order to do so, it's now included in the requirements. If you'd prefer to take a different approach, I can absolutely change this!

Thanks,

Tim