Fix Django 1.10 support, now that django-mptt 0.8.6 is out

Author: vdboor

polymorphic_tree/models.py

@@ -77,7 +77,10 @@ class PolymorphicMPTTModel(with_metaclass(PolymorphicMPTTModelBase, MPTTModel, P
  can_have_children = True
 
  # Django fields
- _default_manager = PolymorphicMPTTModelManager()
+ if django.VERSION >= (1, 10):
+ objects = PolymorphicMPTTModelManager()
+ else:
+ _default_manager = PolymorphicMPTTModelManager()
 
  class Meta:
  abstract = True