Basic autocomplete for admin posts tags

Similar to the skins autocomplete: basic LIKE search, maximum MAX_RECENT items. Can be tweaked by further requests.
Rake task to destroy all unused admin post tags
Issue 3284: Change subject line for account activation emails
Merge branch 'master' into deploy
Updating whitelist and resolving conflict
Merge branch 'master' into deploy
Merge branch 'master' into deploy
Merge branch 'master' into deploy
Merge branch 'master' into deploy
Merge branch 'master' into deploy
Merge branch 'master' into deploy
Merge branch 'master' into deploy
Fixing deploy script for db server
Merge branch 'master' into deploy
Merge branch 'master' into deploy
Merge branch 'master' into deploy
Show 'synonymous' instead of all non canonical tags

Noncanonical tags encompass both unfilterable and synonyms.

There was already a column to show unfilterable tags only.

The 'noncanonical' column was showing unfilterables and tags that had been merged with synonyms (mergers).

Now there is a 'synonymous' column instead, which shows only non-canonical tags that have synonyms.
When sorting by taggings count, also provide secondary sorting by name

Taggings count don't provide enough order - when too many tags have the same number of uses, the results of sorting are unpredictable and the order keeps changing.

This adds secondary sorting by name, ascending, when the taggings count is the same.
Merge branch 'master' into deploy
Merge branch 'master' into deploy