Updates to support Xcode 6.1 Beta 2

Xcode 6.1 introduced changes to Swift that caused Nimble compilation to fail. In particular:

* File names within a module must be unique, since it uses the file names to distinguish private members. Nimble had two files named Protocols.swift.

* It is no longer possible to add public extensions to types defined in another module. This caused Nimble to fail, since it included an extension to Optional to make it conform to the Printable protocol.

This PR fixes these issues and allows it to be used with the latest beta.