In Django 1.8, they've added a fixtures attribute to TestCase which

defaults to None. This messes up our existing code that expects test cases

that don't have fixtures to just not have this attribute defined.
We can't just change it to default to an empty list, because django's

TestCase then gets grumpy. Instead, I've changed it so we handle a None

value appropriately.

Ran djblets unit tests on 1.6 and 1.8.
Ran Review Board unit tests on 1.6 and 1.8.