Disambiguate ObjC from M and Matlab

Check if data contains common things found in Obj-C. If it is then also do
some additional checks to make sure it's not possibly Matlab or M. If it is
just add them as a precaution.

This is a solution for https://github.com/github/linguist/issues/1025
@ScrimpyCat I think the convention here is `disambiguate_<shared extension>` ;)