bug#55778: 29.0.50; [PATCH] M-. into a .gz; we've all been there.

[Eli Zaretskii]

> Cc: 55778@debbugs.gnu.org, Stefan Monnier <monnier@iro.umontreal.ca>
> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Sun, 05 Jun 2022 15:49:04 +0200
> 
> So I've now added a new command `find-sibling-file' to Emacs 29.  This
> setting does what the latter:
> 
> (setq find-sibling-rules
>       '(("\\(/usr/share/emacs.*/\\(lisp/.*.el\\).gz\\)"
>        "/home/larsi/src/emacs/trunk/\\2\\'")))

We already have ff-find-related-file, why not expand that facility
instead?  the new command sounds like a subset of what
ff-find-related-file can do.