swift234

[ClangImporter] Resolve generated header protocols to native decls as well.

This is the same as the previous commit, but for protocols. To do this I
had to modify the ObjC printer to include a SWIFT_PROTOCOL annotation like
the SWIFT_CLASS annotation already in use. This is probably a good thing
anyway.

Second half of <rdar://problem/16296027>

Swift SVN r14985