small ui freeze break for the user panel

[Matthias Clasen <matthias clasen gmail com>]

I'd like to commit the patch in
https://bugzilla.gnome.org/show_bug.cgi?id=681769
which adds a small greed circle over the avatars in the list to
indicate which users are currently logged in.

http://bugzilla-attachments.gnome.org/attachment.cgi?id=222947 shows
how it looks.

As far as I can tell, we don't have any screenshots of this panel in
either user guide or release notes.