bug#15339: 24.3.50; Control characters are displayed as square in describe-char

[Xue Fuqiao <xfq.free@gmail.com>]

To reproduce:

  emacs -Q
  C-q C-l
  C-u C-x =

In the *Help* buffer, the ‘decomposition’ property of this character
(should be itself, I believe) is displayed as a square, but the
character is displayed right (^L) in the *scratch* buffer.  I also tried
^M, ^G, ^H, ^V, and ^[; the results are the same.


In GNU Emacs 24.3.50.1 (x86_64-apple-darwin12.4.0, NS apple-appkit-1187.39)
 of 2013-09-07 on xfq.local
Bzr revision: 114163 eggert@cs.ucla.edu-20130907002056-0jom28xr5402rpm9
Windowing system distributor `Apple', version 10.3.1187
Configured using:
 `configure --with-ns --enable-checking --disable-silent-rules'

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Help

Minor modes in effect:
  tooltip-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
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-q C-l C-b C-u C-x = C-x o SPC <escape> x r e - e
m - b u <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Type C-x 1 to delete the help window, C-M-v to scroll help.
Char: C-l (12, #o14, #xc) point=192 of 192 (99%) column=0

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils pp wid-edit cl-loaddefs cl-lib descr-text
help-mode easymenu time-date tooltip ediff-hook vc-hooks lisp-float-type
mwheel ns-win 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 ns multi-tty emacs)


-- 
Best regards, Xue Fuqiao.
http://www.gnu.org/software/emacs/