"denet" format save error message

[Kevin Ryde]

Starting from emacs -Q,

        C-x C-f /tmp/x
        "a
        M-x format-decode-buffer denet
                (turns "a into dieresis ä)
        C-x C-s

gives an error

        Wrong number of arguments: #[nil "\300\301!\207" [error "This format is 
read-only; specify another format for writing"] 2 
("/usr/share/emacs/22.0.95/lisp/international/iso-cvt.elc" . 17271) nil], 3

I don't think denet format is meant to be saved, but the error on
attempting isn't clear.

I guess `iso-cvt-read-only' which is used for the denet entry in
format-alist should have some parameters to satisfy the call.
Probably `iso-cvt-write-only' likewise, if it's meant to be a dummy
decode func, though it doesn't seem to be used currently.


In GNU Emacs 22.0.95.1 (i486-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2007-03-03 on pacem, modified by Debian
 (Debian emacs-snapshot package, version 1:20070302-1)
configured using `configure  '--build' 'i486-linux-gnu' '--host' 
'i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' 
'--libexecdir=/usr/lib' '--localstatedir=/var' '--infodir=/usr/share/info' 
'--mandir=/usr/share/man' '--with-pop=yes' 
'--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/22.0.95/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/22.0.95/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/22.0.95/leim'
 '--with-x=yes' '--with-x-toolkit=athena' '--with-toolkit-scroll-bars' 
'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN 
-DSITELOAD_PURESIZE_EXTRA=5000 -g -O2''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_AU
  locale-coding-system: iso-8859-1
  default-enable-multibyte-characters: t