(Bug 4858) Fix detection of fully expanded comments

We changed the HTML structure, but not the way the JS was looking for
whether the element was expanded when it was copied over to the page.
This broke our ability to check that said comment had already been
copied over (and thus did not need to be recopied). Fixing should make
that more efficient.

This also broke the quick reply(!) in the case where you expand a
comment deep in the thread, hit reply to that, change your mind and
decide to read more of the thread (expanding the comment). The
unnecessary replacement removes #qrdiv and breaks it for the entire
page. This'll fix it.
Merge pull request #240 from afuna/expander-replaces-too-much-bug4858

(Bug 4858) Fix detection of fully expanded comments