bug#75398: 30.0.93; files.el documentation refers to "ITS-id" version control

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Mon, 6 Jan 2025 11:15:26 -0600
> Cc: 75398@debbugs.gnu.org, "Eric S. Raymond" <esr@thyrsus.com>
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Stefan Kangas <stefankangas@gmail.com>
> >> Date: Mon, 6 Jan 2025 09:46:02 +0000
> >>
> >> Severity: wishlist
> >>
> >> In files.el, I read this:
> >>
> >>     ;;; Commentary:
> >>
> >>     ;; Defines most of Emacs's file- and directory-handling functions,
> >>     ;; including basic file visiting, backup generation, link handling,
> >>     ;; ITS-id version control, load- and write-hook handling, and the like.
> >>
> >> I understand that "version control" refers to backup files rather than
> >> VCS, but what is "ITS-id"?  I can't find any references to that in the
> >> manual, or by grepping, but since the text was written in 1993, is it
> >> possible that it refers to "Incompatible Time-Sharing System"...?
> >
> > Yes, I think ITS was the system which introduced numbered backup
> > files.  Maybe someone else (Richard?) could confirm.
> >
> > This commentary was added by Eric Raymond in March 1993.
> 
> The question is how do we update this comment to be relevant in 2025.

I'd replace "ITS-id version control" with "version control for
numbered backup files".