bug#23252: 24.5; message-mode: "Show Hidden Headers" doesn't redisplay headers

[David Bremner <david@tethera.net>]

1) emacs -Q
2) M-x message-mail
3) Add a header that will be hidden by default, I tested with
"References: <foo@example.com>"
4) Evaluate "(message-hide-headers)" in the message-mode buffer.
5) Now run C-x n w (or select "Show hidden headers" from the Field menu)
6) Observe no visible change
7) Run M-x message-sort-headers (C-c C-o)
8) Observe your hidden header is now shown.



In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.6)
 of 2016-01-22 on binet, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11802000
System Description:	Debian GNU/Linux testing (stretch)

Configured using:
 `configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.5/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.5/site-lisp:/usr/share/emacs/site-lisp
 --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.5/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.5/site-lisp:/usr/share/emacs/site-lisp
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars
 'CFLAGS=-g -O2 -fstack-protector-strong -Wformat
 -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Important settings:
  value of $LANG: en_CA.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Message

Minor modes in effect:
  mml-mode: t
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  auto-fill-function: message-do-auto-fill
  transient-mark-mode: t
  abbrev-mode: t

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set
Quit
nil
You can run the command `message-sort-headers' with C-c C-o

Load-path shadows:
None found.

Features:
(shadow mail-extr emacsbug sendmail sort gnus-util message format-spec
rfc822 mml easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse
rfc2231 rfc2047 rfc2045 ietf-drums mm-util help-fns mail-prsvr
mailabbrev mail-utils gmm-utils mailheader time-date tooltip electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list newcomment lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
minibuffer nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
dbusbind gfilenotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 75401 14582)
 (symbols 48 17600 0)
 (miscs 40 56 248)
 (strings 32 9152 4333)
 (string-bytes 1 250220)
 (vectors 16 9653)
 (vector-slots 8 389162 14346)
 (floats 8 66 359)
 (intervals 56 273 32)
 (buffers 960 13)
 (heap 1024 49219 818))