Fix .proto files with unicode characters in the comments. (Problem found in '_same_contents')

Testing Done:
Updated unit tests, added a testproject example.

I tried naming the .proto file with a utf-8 character and it failed miserably. Fortunately I don't have that case, so I didn't try to fix it.

Bugs closed: 792

Reviewed at https://rbcommons.com/s/twitter/r/1330/
Sync of https://github.com/pantsbuild/pants/commit/e8dde95941343d6e65eda937ec752fcd2006cdfb