bug#2837: 23.0.91; tramp: ssh passphrase vs. password

Just now I tried to open /ssh:dhcp98:/ and it asked me for "dhcp98's
password".  It *should* have asked me for the passphrase for one of my
SSH keys (id_rsa).  This either means that the prompt is misleading
(i.e. it wants my passphrase) or worse, that it genuinely wants to use
password-based authentication (i.e. ignoring my key).

In GNU Emacs 23.0.91.1 (i486-pc-linux-gnu)
 of 2009-03-30 on elegiac, modified by Debian
 (emacs-snapshot package, version 1:20090329-1)
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/23.0.91/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.0.91/site-lisp:/usr/share/emacs/site-lisp' '--with-x=no' '--without-dbus' '--without-sound' 'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -DSITELOAD_PURESIZE_EXTRA=5000 -g -O2' 'LDFLAGS=-g -Wl,--as-needed' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  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.utf8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: rcirc

Minor modes in effect:
  rcirc-track-minor-mode: t
  savehist-mode: t
  shell-dirtrack-mode: t
  icomplete-mode: t
  partial-completion-mode: t
  show-paren-mode: t
  delete-selection-mode: t
  use-hard-newlines: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-g C-g C-g C-x C-f C-f ESC O A C-g C-x C-f / s C-g 
ESC x r e p o r t SPC e m a c s SPC b u g RET

Recent messages:
Saving file /home/twb/.newsrc.eld...
Wrote /home/twb/.newsrc.eld
Saving /home/twb/.newsrc.eld...done
Loading tramp...done
Tramp: Opening connection for dhcp98 using ssh...
Tramp: Waiting 60s for local shell to come up...
Tramp: Sending command `ssh dhcp98   -q -e none && exit || exit'
Tramp: Waiting for prompts from remote shell
Tramp: Sending password
Quit [4 times]
Quit