Broken Tox + Errors running under Django 1.6

We need to fix a few things to be 1.6 compatible.
  - Tox setup needs to be tweaked due to the new test runner expecting a full import path

- The move in 1.6 to using the new django.db.models.fields.related.ForeignObject baseclass for related fields means that repoint is broken as ForeignObject takes different arguments to `__init__`

- <del>Testing against our app seems to show an issue with the instantiation of Foreign Keys used by a derived class. The base classes Deferred keys are converted to ForeignKeys as expected but the derived class while having the correct descriptor object containing the ForeignKey object doesn't have the new field added to _meta.fields. Assume this is due to changes in the m2m filling routines / cache update code. Will need to investigate.</del>