Fix for PolyModel type lookup
Fix for PolyModel type lookup

Note:
When using graphene Interfaces, previous implementation could
display false positives by only checking if the root type matches
with the given model. Now if you pass in an Interface type, the
check will check that the object type's class hierarchy is a subset of
the instance's class hierarchy

graphql-python/graphene-gae,ekampf/graphene-gae