bug#42406: Mouse-wheel scrolling can be flickering

[martin rudalics]

> Let me reply that, with the three critical instances of
> wset_updated_mode_line just out-commented, when I scroll in a frame
> _with_ input focus, then the mode line is always correctly updated.

Because scrolling can change lots of other things in the selected window
so this is probably expected.

> If
> I scroll in a frame without input focus, then at least the percentage
> is always updated, and the line-number is update as soon as the
> (hollow) cursor reaches the top or the bottom of the range of text
> shown in the frame. In any case, with global-line-numbers-mode on, is
> there a situation where, in practice, one needs to look at the line
> numbers as shown in the mode line?

I hardly ever look so I can't tell.  But doing the substitutions I
suggested earlier can hardly harm IMO.  And if they harm, then we'd yet
have another issue to investigate.

martin