fix tag cloud implementation to use external values (value attributes) that map 1-to-1 with internal values (TagIds)
Bugfix: rethreading moves tags and tickets now

This deals with most of SD-231

Need to also redirect for moved comments when linked directly.

I don't think we *know* of any other problems that would fall under
SD-231, but we should probably do a more through inventory before
closing it.
Merge branch 'master' of https://github.com/wolftune/snowdrift
Merge github.com:strbean/snowdrift
Merge github.com:dlthomas/snowdrift