bug#9840: 23.3; rmail-edit-current-message destroys MIME messages [SEVERE]

[Mark Lillibridge <mark.lillibridge@hp.com>]

    In gnuemacs 23.3.1 (or earlier?), displaying of MIME text parts got
turned on by default.  E.g., buttons like:

[1/1:text/plain Hide]

appear in the message body displayed followed by the decoded text part.

    When you invoke message editing via 'e', rmailedit.el assumes
(mistakenly) that it is dealing with a normal message body (e.g., not
decoded) and lets you edit the buttons and decoded text.  Far, far
worse, when you finish editing, rmailedit.el replaces the original valid
message with the decoded text!  This destroys all the nontext parts and
put the button text in the message itself.  Worse, if you realize
something is wrong and attempt to abort the edit via ^c^[, your message
is still destroyed since rmail-abort-edit just restores the "message
text" (e.g., the decoded view) then calls the normal edit exit code
(rmail-cease-edit).  To add to the fun, if you attempt to abort editing
by killing the rmail buffer, you will lose any other changes made to
that mbox file, including the incorporation of new mail.

Executive summary: if you press 'e' (even accidentally) in Rmail mode
while viewing a MIME message, it will be destroyed the matter what you
do.

- Mark