Fixture teardown not working with Django 1.7

[daineX]

As of Django 1.7 ConnectionRouter's allow_syncdb has been renamed to allow_migrate:
django/django@12e9804

This causes an AttributeError in https://github.com/django-nose/django-nose/blob/master/django_nose/fixture_tables.py#L124 which in turn causes tables_used_by_fixtures to always return an empty set.

Because of this, fixtures will not be reverted correctly, leaving data behind between tests.