Revert get_real_concrete_instance_class_id() dry attempt
Revert get_real_concrete_instance_class_id() dry attempt

Caused by f9fffc44c12ebb524ddf002e6fd5f9d221f36f7a

skirsdeda/django_polymorphic,chrisglass/django_polymorphic,chrisglass/django_polymorphic,skirsdeda/django_polymorphic,skirsdeda/django_polymorphic