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

[martin rudalics <rudalics@gmx.at>]

 > 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