djangomod.command: allow non-"--"-options

**Please don't merge yet**
*Travis won't run on my fork, so I need to see if this fixes all the issues once travis ran the tests. So, this is rebase-land ;)*

Makes djangomod more consistent with django-admin.py's usage:

```
$ django-admin.py --help
Usage: django-admin.py subcommand [options] [args]
```

(also fixes failing loaddata test)