(message-frames): New custom group.

(message-frames): New custom group.
(message-original-frame): New variable.
(message-use-multi-frames): New variable.
(message-delete-frame-on-exit): New variable.
(message-send-and-exit): Delete frame which made for editing message.
(message-kill-buffer): Ditto.
(message-delete-frame): New function.
(message-pop-to-buffer): Make new frame when edit message.