bug#42406: Mouse-wheel scrolling can be flickering

[martin rudalics]

> Performance does not degrade when only the two calls of
> wset_update_mode_line you mentioned are commented out. However, with
> just commenting out these two instances, I still have a scroll
> performance problem when scrolling by using the scroll-bars. Could you
> also identify the instance concerning this?

I forgot how Emacs precisely handles that.  Maybe Eli can tell.

martin