bug#22395: 25.0.50; 'C-v' scrolls only a half of the window height

[martin rudalics]

> Recipe from "emacs -Q":
>
> 1. Eval:
>      (setq scroll-preserve-screen-position t)
>      (setq scroll-margin 2)
>
> 2. Visit the attached file.
>
> On my system, I initially see lines 1 to 33.
>
> 3. Type 'C-v'
>
> I observe that 'C-v' has scrolled the buffer vertically, but only by
> about a half of the window height (I now see lines 16 to 48).
> Subsequent 'C-v' commands do the same: they scroll the buffer by a
> half of the window.
>
> This seems wrong.  The amount of scrolling should be "a near full
> screen", as described in 'C-h k C-v'.
>
> I observe this bug also in the last 24.5 release.

I'm not sure whether it's a bug or a feature.  But here I can "fix" your
behavior by customizing ‘scroll-conservatively’ to 101.

martin