* wl-summary.el (wl-summary-buffer-thread-modified):

    * wl-summary.el (wl-summary-buffer-thread-modified):
        New buffer-local variable.
        (wl-summary-set-thread-modified): New function.
        (wl-summary-thread-modified-p): New function.
        (wl-summary-save-status): Use function `wl-summary-thread-modified-p'.
        (wl-summary-yank-saved-message): Use function
        `wl-summary-set-thread-modified'
        (wl-summary-switch-to-clone-buffer): Add
        `wl-summary-buffer-thread-modified'.
        * wl-vars.el (wl-summary-buffer-message-saved-hook): New variable.
        (wl-summary-buffer-mark-saved-hook): Ditto.
        * wl-summary.el (wl-summary-msgdb-save): New hook
        `wl-summary-buffer-message-saved-hook' and
        `wl-summary-buffer-mark-saved-hook'.