UserChangeForm.user_permissions should select_related content_type

This was causing hundreds of queries to fetch each ContentType
individually.
(cherry picked from commit c99e46c684aa9356f6d45bad3a2f4c132219487f)
Version 0.1.2
Changes for 0.1.2
(cherry picked from commit bbba93e8b2734582e69153a7d1292f0250e73a9b)