bug#4080: 23.1.50; Message-mode doesn't handle YANK-ACTION argument of COMPOSE-MAIL

Command compose-mail has an optional sixth argument YANK-ACTION which
defines what to do when user presses C-c C-y (mail-yank-original) in
mail-mode buffer. Here's a simple test suite:

    (let ((mail-user-agent 'sendmail-user-agent))
      (compose-mail user-mail-address "Test" nil nil nil
                    (list (lambda (&rest args)
                            (insert (format "%s\n" (car args))))
                          "Body")))

After evaluating the above code press C-c C-y in the mail-mode buffer to
see text "Body" appear. It should work nicely.

However, this does not work when mail-user-agent is "message-user-agent"
or "gnus-user-agent". Message-mode has C-c C-y (message-yank-original)
command but it does not do anything.

Here's the same test suite with message-user-agent as the
mail-user-agent:

    (let ((mail-user-agent 'message-user-agent))
      (compose-mail user-mail-address "Test" nil nil nil
                    (list (lambda (&rest args)
                            (insert (format "%s\n" (car args))))
                          "Body")))

C-c C-y doesn't do anything.


---------------
In GNU Emacs 23.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.12.12)
 of 2009-08-08 on mithlond