swift234

Add manglings for associated types.

This should allow declarations inside protocols to mangle successfully, which is needed by SourceKit to be able to use mangled names as unique decl identifiers. I'm also planning to use mangled protocol decls to name generic curry thunk symbols.

This only introduces a mangling for independent associated types. I think we will eventually want to mangle dependent associated types (such as T.AssocType for an archetype T : SomeProtocol) with a non-indexed mangling too, but this doesn't do that yet.

Swift SVN r8148