add support for django 1.11 replacing model._meta.get_field_by_name (#21489)

src/authentic2/utils.py

@@ -620,7 +620,11 @@ if django.VERSION < (1, 8, 0):
     def get_fk_model(model, fieldname):
         '''returns None if not foreignkey, otherswise the relevant model'''
         try:
-            field_object, model, direct, m2m = model._meta.get_field_by_name(fieldname)
+            # https://docs.djangoproject.com/en/1.11/ref/models/meta/#migrating-from-the-old-api
+            field_object = model._meta.get_field(fieldname)
+            model = field_object.model
+            direct = not field_object.auto_created or field_object.concrete
+            m2m = field_object.many_to_many
         except FieldDoesNotExist:
             return None
         if not m2m and direct and isinstance(field_object, ForeignKey):