Added django_manage command=raw with raw_command and raw_args parameters

Allows any command, wrapped in the virtualenv, pythonpath, app_path, and settings magic of the rest. This will give it some future proofing.

I'm using it for South commands for the moment until I get a little time to write an actual version. I'm thinking a separate django_south module because it's more capable of going state/idempotent than manage.py is. South has commands to introspect the current state of a migration before doing anything, unlike manage.py in general.