Re: jit lock sit-for provokes redisplay provokes imenu

[Richard Stallman <rms@gnu.org>]

Rather than increment CHARS_MODIFF separately,
it should copy the value from MODIFF.
That way, values of CHARS_MODIFF will be comparable with values
that were copied from MODIFF.

Also, instead of setting CHARS_MODIFF explicitly in each place that
modifies the buffer, modify_region could set it from MODIFF, and
changing text properties could save and restore it to prevent it from
being incremented.  That means changes in fewer places, and no need
for each place that modifies the buffer to know about CHARS_MODIFF.