Make importing URLs from installed apps work.

Hi,

I couldn't see how this used to work?

For example, with django.contrib.auth in installed_apps, the relevant configured URLs were:
```
^django.contrib.auth/
```

Whereas with this patch applied, they look like this:
```
^login/$ [name='login'] 
^logout/$ [name='logout'] 
^password_change/$ [name='password_change'] 
^password_change/done/$ [name='password_change_done'] 
^password_reset/$ [name='password_reset'] 
^password_reset/done/$ [name='password_reset_done'] 
^reset/(?P<uidb36>[0-9A-Za-z]{1,13})-(?P<token>[0-9A-Za-z]{1,13}-[0-9A-Za-z]{1,20})/$ [name='password_reset_confirm'] 
^reset/done/$ [name='password_reset_complete']
```

Not sure what original functionality this patch breaks, so will need review!