bug#8308: 23.3; Use utf-8 for writing abbrev file

[Eli Zaretskii <eliz@gnu.org>]

> From: Leo <sdl.web@gmail.com>
> Date: Mon, 21 Mar 2011 18:01:17 +0800
> Cc: 
> 
> Would you agree to use utf-8-emacs instead, which covers all characters.

That's better, but the characters outside Unicode are still going to
do bad things to any software except Emacs.  AFAIK, emacs-mule is a
superset of iso-2022 in the same way as utf-8-emacs is a superset of
utf-8.

> > Can you tell what is the purpose of this change?
> 
> Make abbrev file editable to other editors.

If we are really keen on making the abbrev files editable to other
editors, we should make sure they are encoded in some encoding that
these other editors will understand.  That probably calls for using
utf-8 for everything that's covered by Unicode, and using other
appropriate encodings for characters outside Unicode.