bug#16449: 24.3.50; emacs hangs while deleting comment in xml file with flyspell-mode on

[Levin Du <zslevin@gmail.com>]

1. Starting from `emacs -Q'

2. open a xml file with contents shown below:

<?xml version="1.0" encoding="UTF-8"?>
<window>
  <control>
    <!--<visible>Player.HasAudio + !Skin.HasSetting(homepageMusicinfo)</visible>-->
    <visible>false</visible>
  </control>
</window>

3. Turn on flyspell mode with `M-x flyspell-mode'

4. Move the cursor to the comment start '<!--', then begin to delete
 comment start chars with C-d. When the line changes to :
    <visible>Player.HasAudio + !Skin.HasSetting(homepageMusicinfo)</visible>-->

   Emacs hangs.
   
In GNU Emacs 24.3.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.17)
 of 2014-01-15 on DuJingwu
Windowing system distributor `The X.Org Foundation', version 11.0.11303000
System Description:	Ubuntu 13.04

Configured using:
 `configure --with-x-toolkit=gtk2 'CFLAGS=-O0 -g3''

Important settings:
  value of $LC_CTYPE: zh_CN.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  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
  transient-mark-mode: t

Recent input:
M-x g n u - <backspace> - <tab> <tab> b u <tab> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
C-g C-g C-g <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<menu-bar> <help-menu> <send-emacs-bug-report>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...
Quit [3 times]
call-interactively: End of buffer

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
help-fns mail-prsvr mail-utils help-mode easymenu time-date china-util
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)