Remove getCallback indirection in modules
Instead, assume that the imported module contains the Callback class
that was previously returned by getCallback. This is done to prevent
a circular import (caused by the __init__ importing a submodule).
"""
>>> from django.contrib.sites.models import Site
>>> from django.conf import settings
>>> Site(id=settings.SITE_ID, domain="example.com", name="example.com").save()
>>> # Make sure that get_current() does not return a deleted Site object.
>>> s = Site.objects.get_current()
>>> isinstance(s, Site)
True
>>> s.delete()
>>> Site.objects.get_current()
Traceback (most recent call last):
...
DoesNotExist: Site matching query does not exist.
"""