Use Python 3 compatible MySQL database adapter

This fork is in alpha, but apparently the best that's possible at the
moment. It's recommended in the Django docs:
https://docs.djangoproject.com/en/1.6/ref/databases/#python-3
Disallow failing tests with Python 3 and Django 1.7

This marks the end of my work on Django 1.7 and Python 3. Support for
both can now be considered stable.