bug#23833: 24.5; assoc-string with CASE-FOLD may fail

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Thu, 23 Jun 2016 08:26:22 -0400
> Cc: 23833@debbugs.gnu.org
> 
> assoc-string uses compare-strings, which uses upcase to ignore case,
> but upcase is not always the inverse of downcase:
> 
> (upcase (downcase "DZ")) ;=> "Dz"
> ;; Or to put it another way
> (= (upcase (downcase ?\u01F1)) ?\u01F2) ;=> t
> 
> Same behaviour seen in emacs-25 and master

Thanks.

This is a documentation issue: both 'assoc-string' and
'compare-strings' had inaccuracies in their doc strings.  I fixed this
on the emacs-25 branch, and I'm marking this bug done.