Several fixes for the "This tag is under discussion" notice on the post
index page:
* Fix the notice appearing for BURs that aren't pending.
* Fix the notice never going away because of the cache never expiring.
* List all topics when a tag is involved in multiple BURs.
* Link to the forum post instead of the forum topic (fix#4421).
* Optimization: don't check for BURs when the search isn't a simple
single tag search.
* Add a `tags` field to the bulk update requests table for tracking all
tags involved in the request (excluding tags in mass updates that are
negated/optional/wildcards). Known issue: doesn't handle tag type
prefixes in mass updates correctly (e.g. `mass update foo -> artist:bar`
doesn't detect the tag `bar`).
* Allow searching the /bulk_update_requests page by tags.
We don't really need to cache the notice here, but we do it anyway to
reduce queries on the post index page.
* Fix inconsistencies in how wiki pages were linked.
* Link directly to the wiki instead of to a title search that is expected
to redirect to the wiki.
Fineprint text was variously styled with `.info`, `.tn`, `.hint`, or
`.cost-footnote` css classes. Standardize on `.fineprint` instead. Use
`.hint` only for form hints and `.tn` only for <tn> tags in translation
notes.
Incidentally changes the font size of form hints to 0.8em (was 0.7em)
and the color of fineprint to #888 (was #AAA or #666).
* Move the limit:<n> / order:random metatag parsing from the controller
to the post set.
* Introduce `Tag.has_metatag?` and use it to parse these metatags
instead of using a regex (#2894).
