Fix InheritanceManager when the model has a self reference.

Otherwise, we reach max recursion depth.

model_utils/managers.py

@@ -106,6 +106,7 @@ class InheritanceQuerySetMixin(object):
             rel for rel in model._meta.get_all_related_objects()
             if isinstance(rel.field, OneToOneField)
             and issubclass(rel.field.model, model)
+            and model is not rel.field.model
             ]
         subclasses = []
         if levels:

model_utils/tests/models.py

@@ -25,6 +25,7 @@ class InheritanceManagerTestParent(models.Model):
     related = models.ForeignKey(
         InheritanceManagerTestRelated, related_name="imtests", null=True)
     normal_field = models.TextField()
+    related_self = models.OneToOneField("self", related_name="imtests_self", null=True)
     objects = InheritanceManager()
 
     def __unicode__(self):