bug#4623: 23.1.50; rmail changes encoding of characters on save

[Markus Rost <rost@math.uni-bielefeld.de>]

The crucial thing is that the mbox file after reading and saving in
rmail differs from the original file only by some headers, usually
X-RMAIL-ATTRIBUTES, X-RMAIL-KEYWORDS.

Your patch fixes the problem.

> I think it
> should be done in a manner similar to the following, since saving an
> rmail file with just "C-x C-s" should work.

Yes, your patch is better than my attempts, as in

<URL:http://lists.gnu.org/archive/html/bug-gnu-emacs/2009-10/msg00052.html>

and at the end of

<URL:http://lists.gnu.org/archive/html/bug-gnu-emacs/2009-10/msg00182.html>

However all 3 patches leave the same problem, namely that the rmail
buffer gets the buffer-file-coding-system 'no-conversion.  This can be
easily seen from the mode line indicator ('=' instead of say '1' or
'u').  See the detailed discussion in the second part of

<URL:http://lists.gnu.org/archive/html/bug-gnu-emacs/2009-10/msg00182.html>

Now this problem is of minor importance, at least I don't know of any
serious effects, and refreshing the rmail buffer by hitting "Nj"
(where N is the message number you are looking at) resets the
buffer-file-coding-system (and the mode line indicator).

One could work around this by calling

(rmail-show-message rmail-current-message)

after the save, although this isn't satisfactory.

Anyway, I think that your patch should be installed.