Merge branch 'no-pil'

Conflicts:
	MANIFEST.in
	README.md
	setup.py
updating tox envs to use PIL
trying to get pil working on travis ci
Organize imports
Add a fixme to mocked files
Remove redundant __doc__ assignment
Compare version with tuple
Regression test for pointing model as unicode
Add tests for finding model with a class and app.model string
Add support to load models without app name
Raise exception on ambiguous model name.

If 2 apps have models with the same name we can't
get the model without the app name.
Cache models for faster loading without app name
Extract the logic of finding a model to ModelFinder
Adapt the "model not found" test.

I don't think we need to check the exception message.
It's only used in one place. It won't change.
Comment to explain why there is only one MommyFinder instance.
Group MoldelFinder tests
Update README