bug#27353: 25.2; rmail corrupts encoded message if you edit headers

[Ken Olum <kdo@cosmos.phy.tufts.edu>]

If you use rmail edit to change any header in an message with nontrivial
transfer encoding, parts of the header will get encoded, not just the
body.  The problem is that the reencoding system in rmail-cease-edit
uses (point), but the previous call to rmail-edit-update-headers changes
(point), unless no headers are modified.

Even if you don't yourself modify any headers, bug#26918 can cause there
to be a new content-type header, triggering this problem.

I'll send a patch to fix this bug and #26918.

                                        Ken

In GNU Emacs 25.2.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2017-06-08 built on cosmos
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description:	Ubuntu 14.04.5 LTS

Configured features:
XPM JPEG TIFF GIF PNG SOUND NOTIFY LIBXML2 FREETYPE XFT ZLIB
TOOLKIT_SCROLL_BARS LUCID X11

Important settings:
  value of $LC_ALL: C
  value of $LANG: en_US.UTF-8
  locale-coding-system: nil

Major mode: Lisp Interaction

Minor modes in effect:
  shell-dirtrack-mode: t
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  tooltip-mode: t
  global-eldoc-mode: t
  mouse-wheel-mode: t
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  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t

Recent messages:
Loading /home/kdo/emacs-init.el (source)...done
Loading /home/kdo/emacs-init-mail.el (source)...done
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
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mwheel x-win term/common-win x-dnd tool-bar dnd fontset image regexp-opt
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page menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock
font-lock syntax facemenu font-core frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
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sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote inotify dynamic-setting
font-render-setting x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 105422 9891)
 (symbols 48 21581 3)
 (miscs 40 64 121)
 (strings 32 20808 4178)
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 (vectors 16 14339)
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 (buffers 976 18)
 (heap 1024 41469 1008))