Issue #1022404 by Berdir, te-brian: Added drag and drop sorting for list display fields and replaced header theme functions with a hook.

Issue #750566 by Berdir, manarth: Added message delete changed hook and update privatemsg_thread_change_delete() to work like privatemsg_thread_change_status().

#555016 by Berdir | neriweaver, trupal218, BenK, nbz, archard, nilsja, kriskd, Liliplanet, yaz085, litwol, Feet, jaron: Added recipient types, allowing to send messages to roles and other recipient groups.