* The custom manager was not assigned to _default_manager;
get_first_user_defined_manager() always returned None
* The PolymorphicManager couldn't remember it's custom queryset;
a RelatedManager creates a new instance of a manager, so the queryset
parameter should be known at class-level, not object level.
* The old method of providing a custom queryset class has been deprecated.
Diederik van der Boor
78253bfe12