bug#55579: 29.0.50; Abbrevs not saved on exit anymore

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Juri Linkov <juri@linkov.net>,  55579@debbugs.gnu.org
> Date: Wed, 25 May 2022 14:10:31 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> BTW, I noticed that ~/.emacs.d/abbrev_defs
> >> is visited without font-locking.  Here's the fix:
> >
> > Won't that make loading abbrevs slower and more expensive?  that file
> > is normally not edited interactively, only if the user explicitly
> > wants to do so.  So why is font-lock in it important?
> 
> `read-abbrev-file' just uses `load' on the file, so the mode cookie
> doesn't do anything non-interactively.

Then let's have a comment where the cookie is written to explain
that it assumes 'load', and let's have another comment where we load
the file to explain why using another function should consider this
aspect.