rbext historically required a -m parameter to specify modules in the

extension to test, but this wasn't always sufficient. Module names were

just passed to nosetests, and didn't impact the list of installed

apps, meaning that referenced models would fail to import.
To address this, and to simplify usage, there are two new options:


-e/--extension takes a full class path, importing it to find the

  list of installed apps, which will be added to Django. This doesn't

  currently support extension dependencies, but it's not clear that

  anyone has ever used this feature anyway.


--app can be specified multiple times. It takes an app label that

  gets added to Django.


This massively simplifies the ease of use of rbext, and removes almost

all need for a custom settings_local.py file.

Tested rbext test with the rbintegrations and Power Pack codebases,

utilizing both -e and --app. All tests passed without the need for a

custom settings_local.py.