Expose instance model to complete related historical fields

Author: macro1

simple_history/models.py

@@ -182,6 +182,7 @@ def get_instance(self):
             )),
             'history_object': HistoricalObjectDescriptor(model),
             'instance': property(get_instance),
+            'instance_type': model,
             'revert_url': revert_url,
             '__str__': lambda self: '%s as of %s' % (self.history_object,
                                                      self.history_date)
@@ -283,7 +284,7 @@ def get_field(self, other, cls):
     def do_related_class(self, other, cls):
         field = self.get_field(other, cls)
         if not hasattr(self, 'related'):
-            self.related = RelatedObject(other, self.rel.field.model, self)
+            self.related = RelatedObject(other, cls.instance_type, self)
         transform_field(field)
         field.rel = None