The use of raw asserts in unit testing is a bit of an anti-pattern as asserts can be disabled at runtime via python -O.

This PR converts all of these raw assert calls, as well as the use of the eq_ helper function from nose to native self.assertX calls provided by the unittest library. Added a fallback to unittest2 for Python 2.6.

Note: the travis tests are failing because of an unpinned version install on flake8. If you bump travis to rerun master, it will fail for the same reason due to additional checks introduced in flake8 since travis was last run on master.