bug#12927: 24.2; global-hl-line-mode and "scroll-conservatively=1000" take jump up-down the text when hold DOWN key (in *info* buffer).

[Eli Zaretskii]

> From: Oleksandr Gavenko <gavenkoa@gmail.com>
> Date: Sun, 18 Nov 2012 23:13:22 +0200
> 
>   (setq scroll-conservatively 1000)
>   (global-hl-line-mode 1)
> 
> and "C-h i". I press and hold DOWN key. After some time cursor reach end of
> frame and then text scroll up but sometimes it seems as text jump down! And I
> get fill that text moving have jerks.

This is some bad interaction between scroll-conservatively and
window-vscroll, it somehow succeeds to activate code paths that I
never before saw in action.

As a temporary work-around, set auto-window-vscroll to nil.  I will
try to find a better solution when I have time.