Really, the "correct" way to do this is to undo "scrolltheworld", and
then just have a compose div that always lives underneath the message
list div. (This will also allow us to deal much more reasonably with
the whole "Is the composebox in focus" thing.)
In the interest of prototyping something more rapidly, though, we
adopt the somewhat more hackish approach, with the understanding that
much of it will probably be simplified later.
(imported from commit e2754be155c522b6dac28e7b84c62bd2030217c8)
Waseem Daher
Leo Franchi
Reid Barton
Jacob Hurwitz