bug#2228: 23.0.90; rmail-cease-edit ignores changes to the message headers

[Richard M Stallman]

    If one invokes rmail-edit, and edits the headers of the message, the
    changes to the headers are not copied back to the original message
    held in rmail-buffer.  The effect is that your edits of the headers
    are lost after you type "C-c C-c" to exit rmail-edit.

I never got around to writing the code to copy header edits into the
original message.  Perhaps the easiest way to do it is to put the "old
version" into a buffer and compare the edited headers with the old
headers.