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

#968384 by Berdir: Fixed upgrade path from 6.x-1.3+ and cleaned up indexes in existing 6.x-2.x installs.

#979956 by Berdir | IWasBornToWin: Fixed tagging messages on view thread page doesn't work with a %user url prefix.

#850022 by Berdir | BenK: Improved autocomplete for different recipient types and name conflicts between them.

#850552 by Berdir | BenK: Fixed URL for non-existent users shows messages for current logged in user.

#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.

Mega commit: #314327 (message tagging) by nbz, Berdir. #314066 (upgrade path from d5) by Berdir, nbz.