Suggested by Pete Shinners: treat .m and .mm files as source code.
Suggested by Pete Shinners: treat .m and .mm files as source code.

Question for Jack Jansen: is this reasonable?

Candidate for 2.2 release branch (if Jack thinks it's OK).

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator