Clear deprecation warnings, update to new layout

The "new" layout has been around since Django 1.3...
Update to Django 1.5

1. Replace withswitches with a "switch_is_enabled" assignment tag that
better models what is available outside templates;
2. Skip tests where there is a custom User;
3. Remove override_settings, since this is provided since Django 1.4;
4. Explicitly pass in the request processor in tests when they depend
on it.