bug#32002: 24.4; Scroll bar start, end not correct

[Eli Zaretskii]

> Date: Sun, 22 Jul 2018 09:25:20 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: mkupfer@alum.berkeley.edu, 32002@debbugs.gnu.org, kurn@sfu.ca
> 
> My knowledge of what scrolling should do is too limited.

(It seems like I need to put my instructor hat on today ;-)

Let me fill you in: scrolling just needs to set the window's start
point to the desired value, all the rest is done by redisplay.  As
simple as that.

(Well, if you need to scroll more than one screenful, then you need to
worry about a few other things, like setting point such that Emacs
won't scroll back to where point is.  But this is not one of those
cases, we just scroll by one line here.)