Make sure factory_boy 2.0 isn't used

The extract_prefix argument was removed from post_generation as noted at
https://factoryboy.readthedocs.org/en/v1.3.0/reference.html#factory.PostGeneration
Add missing django_libs test requirement
Note dependencies (so tests and install work)
Import multiprocessing to fix strange bug

As noted here: http://bugs.python.org/issue15881#msg170215