Fix #15

This is a hackish monkey patch, but I found no way to do this using plugins.

It fixes the (officially closed) [issue #15](https://github.com/jbalogh/django-nose/issues/15), which I and several other people were still experiencing.

The problem is reproduceable by creating a test-only model and running `./manage.py test` instead of `./manage.py test <appnames>`

This fix changes the `loadTestsFromDir` function in nose.loader.TestLoader from a lazy generator into a regular function returning a list. This makes the test modules along with their modules be imported upfront and thus be seen by Django.