gnus-configure-posting-styles: Use with-silent-modifications

[Christopher Schmidt <christopher@ch.ristopher.com>]

Right at the end of gnus-configure-posting-styles there is this form:

    (when (or name address)
      (add-hook 'message-setup-hook
                `(lambda ()
                   (set (make-local-variable 'user-mail-address)
                        ,(or (cdr address) user-mail-address))
                   (let ((user-full-name ,(or (cdr name) (user-full-name)))
                         (user-mail-address
                          ,(or (cdr address) user-mail-address)))
                     (save-excursion
                       (message-remove-header "From")
                       (message-goto-eoh)
                       (insert "From: " (message-make-from) "\n"))))
                nil 'local))

When the hook is run, the message buffer will be modified and undo
information will be stored in buffer-undo-list.  That does not feel
right.  I think the body forms of this save-excursion should be embedded
in a with-silent-modifications.

        Christopher