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

[Mike Kupfer]

Eli Zaretskii wrote:

> C-v scrolls by a window-full, that's why it signals an error.
> Try "C-u 1 C-v" instead.  That's what the down-stepper
> does, so there's no inconsistency here.

Ah!  Yes, that works.  Thanks for that and for the pointer to
scroll-bar-adjust-thumb-portion.

Though using the Emacs 25 in Debian stable (25.1) and testing (25.2),
the stepper buttons don't seem to be behaving quite right.

With (setq scroll-bar-adjust-thumb-portion t):

  If I go to the bottom of my ~/.profile and start clicking on the
  up-stepper, the text will scroll, but the amount it moves varies from
  0 to 2 lines.  (I expect it to scroll 1 line per click.)

With (setq scroll-bar-adjust-thumb-portion nil):

  If I go to the bottom of my ~/.profile using M->, the last line of the
  file is a couple lines from the bottom of the window.  If I click once
  on the up-stepper, I expect the last line to move closer to the bottom
  of the window.  Instead, it jumps to the top of the window.

If I have time today, I'll try building Emacs 26 with GTK to see if it
behaves any better.

mike