bug#74844: m-buffer: Broken Top Directory node in Info manual due to malformed Texinfo direntry

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> However, the @direntry as
> noted in the "dir" and "m-buffer-doc.info" files is "* m-buffer.doc."

Hmm... yup.
I pushed to Emacs a fix for the generation of that Texinfo element in
`ox-texinfo.el` and to `m-buffer` I pushed another change which tries to
workaround that bug (for when it's used with an older Emacs).

The patch for `ox-texinfo.el` is below.  It's "obviously safe", but
I suspect it's too late for Emacs-30.  Eli?


        Stefan


diff --git a/lisp/org/ox-texinfo.el b/lisp/org/ox-texinfo.el
index 6adee9fca3f..deceeca8947 100644
--- a/lisp/org/ox-texinfo.el
+++ b/lisp/org/ox-texinfo.el
@@ -826,9 +826,7 @@ org-texinfo-template
               ;; `dn' is presumed to be just the DIRNAME part, so generate
               ;; either `* DIRNAME: (FILENAME).' or `* FILENAME.', whichever
               ;; is shortest.
-              ((and dn (not (equal dn file)))
-               (format "* %s: (%s)." dn (or file dn)))
-              (t (format "* %s." file)))))
+              (t (format "* %s: (%s)." (or dn file) (or file dn))))))
        (concat "@dircategory " dircat "\n"
 	       "@direntry\n"
 	       (let ((dirdesc