bug#12600: 24.2.50; linum-mode: line numbers in fringe do not refresh when resizing frame

[Stefan Monnier <monnier@iro.umontreal.ca>]

> When last_modifed_flag is set, the window must be redisplayed.

No: last_modifed_flag is (normally) only set at the end of redisplay, so
the in the future you can check if redisplay is needed by comparing it
with the buffer's modiff.

> assignment.  OTOH when the buffer iself is modified it has to be
> redisplayed anyway because we hardly know where the change happened.

But instead of going through all the windows that display this buffer,
we just change the buffer's modiff, so it will cause all the
(last_modifed_flag == modiff) checks to fail in the windows that display
this buffer.

BTW, I'm interested in display-optimizations because I sometimes suffer
from severe delays, apparently linked to my use of numerous frames.I
haven't dug into yet enough to know really what's going on, but I have
the impression that I hit a pathological case where optimizations end up
completely disabled such that even after as simple commands as C-f (but
which might do more than meets the idea because of things like
hl-line-mode and reveal-mode, maybe) all the windows/frames get
a redisplay.


        Stefan