api_endpoint __get_permissions_class__ missing __name__

with DRF 3.9.1 we have errors for custom permissions with following exception
```AttributeError: OperandHolder instance has no attribute '__name__'```

the `self.pattern.callback.cls.permission_classes` seems to return a mix of classes and instances (e.g. for a subclass of DjangoObjectPermissions)

Start by locating the api_endpoint __get_permissions_class__ implementation and reproduce the reported error with Django REST Framework 3.9.1 and a custom permission based on DjangoObjectPermissions. Check how self.pattern.callback.cls.permission_classes handles permission classes and instances; done means the endpoint no longer raises AttributeError for valid custom permissions.

Written by the indexing model from the issue text.