When run on Python 3, linters such as Pylint and Flake8 will correctly flag __unicode__ and __long__ as _undefined names_ because _compat.py does not currently follow the Python porting best practice [___use feature detection instead of version detection___](https://docs.python.org/3/howto/pyporting.html#use-feature-detection-instead-of-version-detection). This PR allows this project to pass those tests without adding any linter directives.