Merging

I still think the right thing is to not do global changes exactly, but give comments the
ability to attempt to modify them, and have the effective status come from combining them,
where a comment that references another comment can override its changes, and comments that
don't reference each other have a cumulative effect. This then requires that, for each field,
there's a way of combining a bunch of values: take the maximum severity and priority, all of
the assignees, all of the titles, all of the resolutions, and so forth.

That is, somebody reports a bug. Somebody else posts a request for more info, with a flag to
close the bug as "needs info". The first person replies to the post with the info, with a flag
to remove the "needs info" resolution. But first, a third person commits a fix, with a
resolution "fixed in commit X". Since the earlier reply doesn't reference this comment, the
reopen effect doesn't apply to it, so it's left as "fixed in commit X"; then the original
person can confirm it or deny it in a reply to the "fixed" comment.

My contention is that all of the global stuff can be handled like this, and likely handled
better than actually having central values anyway.