Comments: version 2.8 with lots of changes.

Applied a modified version of Alexia E. Smith's patch from bug 51115.

Added schemas for alternative DBMSes; Oracle version doesn't work yet.
Likewise, there's support for creating the tables by running
maintenance/update.php.

Swapped globals to RequestContext in many places.

Moved logging code to the new, 1.19+ format. This will probably break past
log entries, but it's not like they were working that well in the past.
Added logging for comment deletion and introduced a new
$wgCommentsInRecentChanges global that can be set to true to show comment
additions and deletions in Special:RecentChanges. By default they're
logged only to [[Special:Log/comments]].

Added untested Renameuser support. It should probably work, though I'm not
too sure that Comments_block table since there are two user ID and two
user name columns in that table that need updating when a user is renamed.

Fixed CommentsOfTheDay.php to account for the situation where
SocialProfile is not available.

Added token checks to account for cross-site request forgeries (CSRF).
Also ensured that the AjaxFunctions won't perform write queries when the
database is locked.

Fixed JavaScript so that delete/reply/etc. links will work after a partial
refresh (i.e. after you've replied to a pre-existing comment or written a
new top-level comment of your own).

Change-Id: I988eaa1e0dad29a54b44aee6caaaf8febfef03bf