This adds a test for using the new update_fields in the model save method in Django 1.5 and modifies ModelTracker to pass the test.
This isn't ready to merge yet because there is still no test for update_fields when saving the model for the first time and I'm not yet sure how Django models handle that case yet.
I think this is ready for merging.
Add ModelTracker test for save(update_fields=[...])
Fix ModelTracker for obj.save(update_fields=[...])
ModelTracker: check DB after using update_fields
ModelTracker: pass kwargs to parent save correctly
Fixes usage of update_fields in save()
Add test for ModelTracker before first model save