(pmail-edit-mode): Bind buffer-swwapped-with to nil.

(pmail-edit-mode): Bind buffer-swwapped-with to nil.
(pmail-edit-current-message): Save all of buffer as old text.
Clear undo list.
(pmail-cease-edit): Widen first.
Operate in the view buffer; copy edited text back to mbox buffer
and re-encode what was decoded to display the message.
(pmail-abort-edit): Widen first.