Django 1.7 support

* ./runtests.py will now run when Django 1.7 is installed. (I tested back to Django 1.4)
* Cleared up the Django 1.8 warnings.
* Tests will run in Django 1.7. Classes that threw known Django issues, now pass, and print a warning.


From: https://docs.djangoproject.com/en/dev/topics/db/models/#multiple-inheritance

Changed in Django 1.7.
Before Django 1.7, inheriting from multiple models that had an id primary key field did not raise an error, but could result in data loss.