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.
issues - particularly, don't mix with manual pane resizing and be careful when
viewing from multiple clients; generally cycling the layout a few times will
fix most problems. Getting this in for testing while I think about how to deal
with manual mode.
Split window as normal and cycle the layouts with C-b space. Some of the
layouts will work better when swap-pane comes along.
an arbitrary width and height (0 for the default unlimited). This is neat for
emacs which doesn't have a sensible way to force hard wrapping at 80
columns. Also, don't try to be clever and use clr_eol when redrawing the
whole screen, it causes trouble since the redraw functions are used to draw
the blank areas too.
