rendering_1: Don't require EXPOSE events when redrawing the maze.

  * Rather than having XLIB:CLEAR-AREA generate exposure events
and letting the exposure path handle them, don't generate the
exposure events and just kick off the redraw.  This saves a server
round-trip, but also brings the behavior of clearing the window in
line with what CLIM is supposed to provide.
clx-interface: Push use of :frame rather than :window-title deeper.

  * Basically, delay the conversion to a window title until we're
already holding a sheet to which to apply the title...  Because we
want to store the sheet in a slot on the frame once the frame has
a slot available for it.