bug#61708: 28.2; file-modes-symbolic-to-number inconsistency

[Gregory Heytings]

> > (defun symbolic-mode-to-number (mode)
> >   (string-to-number
> >    (replace-regexp-in-string
> >     "[^0]" "1"
> >     (string-replace "-" "0" mode))
> >    2))
>
> Apart from being misnamed, it doesn't handle tTsS.

Yes, that was just a quick PoC.  It doesn't handle the leading letter, 
either.