Allow custom fields to define dependencies for model freezer

[koen.biermans@…]

The field_dependencies method in the freezer (creator/freezer.py) hardcodes the determination of related models for FK, M2M etc fields.

If you have a custom field that needs a dependency, but is not a subclass of one of the django classes, the freezer misses that dependency and does not add the related model definition. It is obviously not difficult to add the related model definition manually into the migration, but it would be nice if a custom field could define a callback to return the dependent models.

[andrew]

I agree - tentatively scheduling for 0.7.2.