Fixing the `objects` and `_base_manager` attributes of `GaeDatastoreUser` in `CustomPermissionsUserModelBackendTest` so that the tests will still work when the project uses a custom user model.
Fixing the `objects` and `_base_manager` attributes of `GaeDatastoreUser` in `CustomPermissionsUserModelBackendTest` so that the tests will still work when the project uses a custom user model.

Really this needs a fix submitting to Django.  Currently, using `override_settings(AUTH_USER_MODEL='custom')` in a project which already uses a custom user model will cause `AttributeError: Manager isn't available; GaeDatastoreUser has been swapped for 'None'` when trying to use the user model's manager.

stucox/djangae,potatolondon/djangae,stucox/djangae,chargrizzle/djangae,martinogden/djangae,b-cannon/my_djae,nealedj/djangae,pablorecio/djangae,nealedj/djangae,leekchan/djangae,wangjun/djangae,grzes/djangae,leekchan/djangae,wangjun/djangae,armirusco/djangae,wangjun/djangae,leekchan/djangae,asendecka/djangae,chargrizzle/djangae,grzes/djangae,jscissr/djangae,SiPiggles/djangae,jscissr/djangae,trik/djangae,kirberich/djangae,armirusco/djangae,kirberich/djangae,potatolondon/djangae,martinogden/djangae,nealedj/djangae,jscissr/djangae,trik/djangae,martinogden/djangae,SiPiggles/djangae,grzes/djangae,chargrizzle/djangae,asendecka/djangae,stucox/djangae,kirberich/djangae,pablorecio/djangae,SiPiggles/djangae,asendecka/djangae,pablorecio/djangae,armirusco/djangae,trik/djangae