[1.7.x] Improved AppRegistryNotReady message.

        Raises an exception if all models haven't been imported yet.

        """

        if not self.models_ready:

            raise AppRegistryNotReady("Models aren't loaded yet.")

            raise AppRegistryNotReady("Models aren't loaded yet. Ensure django.setup() has been called.")

    def get_app_configs(self):

        """