bug#18138: rev. 117587 causes emacs segfault when auto-complete tests are run

[martin rudalics]

> But there is another issue with rev. 117587 not related with emacs
> segfault. Seems that this revision introduced new behaviour that isn't
> documented: now emacs always has a horizontal scroll bar even if
> scroll-bar-mode is switched off. I tested this in following way:
> - compile emacs rev. 117587 and rev. 117586:
> - run
>    emacs -Q
> - then
>    M-x scroll-bar-mode
> - results:
>    117586: has only vertical scroll bar, M-x ... switched it off;
>    117587: has both vertical (usual) and horizontal scroll bars, running
>    M-x ... switching off only vertical scroll bar.

Yes.  Horizontal scrollbars can currently be switched on and off only
via `horizontal-scroll-bar-mode'.  I did not want `scroll-bar-mode'
switching on horizontal scroll bars as well.  We can either use three
terms `horizontal-scroll-bar-mode', `vertical-scroll-bar-mode', and
`scroll-bar-mode' (where the semantics of the latter would change) or
rename `scroll-bar-mode' to `vertical-scroll-bar-mode' keeping a
`scroll-bar-mode' alias and have only two terms.

Please file a separate report where you suggest how to improve that.

Thanks, martin