Fixed #13516 -- Added an internal type definition for AutoFields, so that subclassed fields are handled correctly by the SQL generator. Thanks to manfre for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13540 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/__init__.py

@@ -459,6 +459,9 @@ class AutoField(Field):
         kwargs['blank'] = True
         Field.__init__(self, *args, **kwargs)
 
+    def get_internal_type(self):
+        return "AutoField"
+
     def to_python(self, value):
         if value is None:
             return value