Check if closed review is merged to master

If it is, say so under the big "Finished!" text.
Include user ID (or lack thereof) in review front-page ETag
Remove unnecessary repository name restrictions
Improve description of new upstream in 'review rebased' mails
Don't report unread news for anonymous users

Anonymous users can't read (as in "mark as read") news, so any unread
news would be unread forever.
Increment review serial number when rebasing

For a move rebase it was typically done anyway as part of adding
a commit (equivalent merge or replayed rebase) to the review, even
when that commit is "empty" and not later displayed in the list of
commits on the review front-page.  (Incrementing twice is not a
problem.)

For a history rewrite rebase, however, it was not typically done.