bug#13174: 24.1; comment-region incorrectly handling XML comments already present

[Louis-Dominique Dubeau <ldd@lddubeau.com>]

1. Execute:

$ emacs -Q

2. M-x nxml-mode.

3. Emtpy the buffer.

4. Enter the following text:

<!-- Blah -->

5. Select that text and issue M-x comment-region.

The text becomes: 

<!-- <\!-- Blah -\-> -->

which is invalid XML. Josse van der Plaat has a solution at:

http://emacswiki.org/emacs/mz-comment-fix.el

Using his solution yields:
 
<!-- <!-\- Blah -\-> -->

which is is valid XML.

This is a bug which has been circulating the internet since at least
2004. James Clark reported in 2004 having communicated with the
maintainer of newcomment.el but apparently nothing happened. See this
message:

http://tech.groups.yahoo.com/group/emacs-nxml-mode/message/661

Please integrate Josse van der Plaat's solution to emacs. Thank you.

In GNU Emacs 24.1.1 (x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2012-09-22 on batsu, modified by Debian
Windowing system distributor `The X.Org Foundation', version
11.0.11300000
Configured using:
 `configure '--build' 'x86_64-linux-gnu' '--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/24.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.1/site-lisp:/usr/share/emacs/site-lisp'
 '--with-crt-dir=/usr/lib/x86_64-linux-gnu' '--with-x=yes'
 '--with-x-toolkit=lucid' '--with-toolkit-scroll-bars' '--without-gconf'
 'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fstack-protector
 --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall -O2'
 'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: nXML

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
  line-number-mode: t
  transient-mark-mode: t

Recent input:
M-x n x m l - m o <tab> <return> C-SPC <C-up> C-w <down> 
<down> < ! - - SPC B l a h SPC - - > <return> <up> 
C-SPC <down> M-x <up> <up> <up> <down> C-k c o m m 
e n <tab> - <backspace> r <tab> <return> <help-echo> 
<help-echo> M-x <up> <down> e m a c <tab> b u <tab> 
<tab> <backspace> <tab> <backspace> <tab> <M-backspace> 
<M-backspace> <M-backspace> <M-backspace> r e e <tab> 
<backspace> p <tab> o <tab> r <tab> <return>

Recent messages:
Error during redisplay: (error "Invalid search bound (wrong side of
point)")
Mark set
Illegal char in prolog
byte-code: End of buffer [2 times]
No document element [8 times]
Mark activated
goto-history-element: Beginning of history; no preceding item [2 times]
kill-line: End of buffer
No document element
Making completion list... [2 times]

Load-path shadows:
/usr/share/emacs/24.1/site-lisp/debian-startup
hides /usr/share/emacs/site-lisp/debian-startup
/usr/share/emacs/24.1/site-lisp/dictionaries-common/flyspell
hides /usr/share/emacs/24.1/lisp/textmodes/flyspell
/usr/share/emacs/24.1/site-lisp/dictionaries-common/ispell
hides /usr/share/emacs/24.1/lisp/textmodes/ispell

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 help-mode view newcomment nxml-uchnm rng-xsd
xsd-regexp rng-cmpct regexp-opt rng-nxml rng-valid rng-loc rng-uri
rng-parse nxml-parse rng-match rng-dt rng-util rng-pttrn nxml-ns
easymenu nxml-mode nxml-outln nxml-rap nxml-util nxml-glyph nxml-enc
xmltok time-date tooltip ediff-hook vc-hooks lisp-float-type mwheel
x-win x-dnd tool-bar dnd fontset image fringe lisp-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 loaddefs
button faces cus-face files text-properties overlay sha1 md5 base64
format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process dbusbind dynamic-setting
system-font-setting font-render-setting x-toolkit x multi-tty emacs)