bug#13623: 24.3.50; Redisplay issue with transient-mark-mode

[Stefan Monnier]

>> And I'm not sure this is worth optimizing anyway: region changes are
>> relatively rare and almost always driven by user input, so I don't
>> think redisplay will become significantly faster as result of any
>> optimizations in this area.
> I have a strong suspicion that this also applies to ~50% of xdisp.c
> unless you're on 2400bps tty or remote X connection via 33600bps modem.

For my use case, the optimisations that matter are the ones that avoid
looking at the unmodified (and mostly all iconified) frames when I work
within a frame or switch between two frames (or maybe 3 at most: the
origin, the destination and the minibuffer-only frame).


        Stefan