TypeError due to django-polymorphic version incompatibility #22
Description
Installing the latest master and running the example project, i get this after creating my first node (on the redirect to the changelist):
TypeError at /admin/tree/basetreenode/
get_child_type_choices() takes exactly 1 argument (3 given)
It seems that the latest code for polymorphic_tree.admin.parentadmin.NodeTypeListFilter.lookups is using the more recent polymorphic.admin.PolymorphicParentModelAdmin.get_child_type_choices convention which accepts "request" and "action" arguments. However, this wasn't introduced until after the latest release of django-polymorphic (0.5.6).
setup.py requires 'django-polymorphic>=0.5.5' which causes the TypeError when 0.5.5 or 0.5.6 is installed in this scenario.
What's the solution? Do we check against django-polymorphic's version number? Is that perhaps what was intended with the Django version check? i don't see the relation to Django 1.6, although i could be missing something.