Disable the old _default_manager and _copy_to_model() fiddling.

This no longer works on Django 1.10, which has a new way to find the
default manager

polymorphic/base.py

@@ -71,6 +71,7 @@ class PolymorphicModelBase(ModelBase):
         self.validate_model_fields(new_class)
 
         # create list of all managers to be inherited from the base classes
+        if django.VERSION < (1, 10):
             inherited_managers = new_class.get_inherited_managers(attrs)
 
             # add the managers to the new model
@@ -105,6 +106,7 @@ class PolymorphicModelBase(ModelBase):
 
         return new_class
 
+    if django.VERSION < (1, 10):
         def get_inherited_managers(self, attrs):
             """
             Return list of all managers to be inherited/propagated from the base classes;