Fix deprecation warnings in tests for Django 1.7 ModelForms

In Django 1.7, creating a ModelForm without specifying fields or exclude is deprecated. This is currently done in some localflavor tests. The easiest option would be to use `fields = "__all__"`, but this is not supported in 1.5.

With this update, tests work for me with Django 1.7 on Python 2.7.