Fix South introspection_rules and db connection reference

### What is the problem / feature ?

South introspection rules were still declared as if the models lived within the private codebase this was extracted from.

### How did it get fixed / implemented ?

Changed them to use the `django_unsigned_fields` path instead.

### How can someone test / see it ?

They are actually usable?

*Here is a star trek picture for your troubles...*

![qlivqap2hxkb6c5u5kge](https://cloud.githubusercontent.com/assets/824194/3959089/44413750-2727-11e4-858e-ea6de9b90e24.jpg)