region before poll(2). This reduces (but does not eliminate) the chance of the
attributes not being normal if tmux is disconnected without warning (ssh ~.,
reboot from inside, etc).
decision for whether or not a pane should be drawn out of the layout code and
into the redraw code.
This is needed for the new layout design, getting it in now to make that easier
to work on.
terminal to be switched between several different windows and programs
displayed on one terminal be detached from one terminal and moved to another.
ok deraadt pirofti