bug#14207: 24.2; insert-file-contents clobbers match data

[Aidan Gauland]

If (and only if) the match data is non-nil when `insert-file-contents'
is called, it clobbers the match-data.

To demonstrate:
*** Welcome to IELM ***  Type (describe-mode) for help.
ELISP> (match-data)
nil
ELISP> (equal 
        (match-data)
        (progn 
          (write-region "foo bar baz wiz" nil "/tmp/foo-file")
          (with-temp-buffer (insert-file-contents "/tmp/foo-file"))
          (match-data)))
t
ELISP> (match-data)
nil
ELISP> (search-backward "elisp" nil t)
340
ELISP> (match-data)
(#<marker at 340 in *ielm*> #<marker at 345 in *ielm*>)

ELISP> (equal 
        (match-data)
        (progn 
          (write-region "foo bar baz wiz" nil "/tmp/foo-file")
          (with-temp-buffer (insert-file-contents "/tmp/foo-file"))
          (match-data)))
nil
ELISP> (match-data)
(0 0)

ELISP> 


In GNU Emacs 24.2.1 (x86_64-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2013-04-03 on dimension8, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
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/24.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.2/site-lisp:/usr/share/emacs/site-lisp'
 '--without-gconf' '--with-crt-dir=/usr/lib/' '--with-x=yes'
 '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars'
 'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fstack-protector
 --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall'
 'LDFLAGS=-Wl,-z,relro' '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_NZ.utf8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: IELM

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 i e l m <return> C-y <return> C-y <return> ( m 
a t c h - d a t a ) <return> C-y <return> M-p M-p <return> 
M-p M-p M-p M-p <return> M-p M-p <return> M-< C-n C-p 
C-SPC M-> M-w M-x r e p o r <tab> <return>

Recent messages:
History item: 1
History item: 2
History item: 1
History item: 2
History item: 3
History item: 4
Wrote /tmp/foo-file
History item: 1
History item: 2
Mark set [2 times]

Load-path shadows:
/usr/share/emacs/24.2/site-lisp/debian-startup hides 
/usr/share/emacs/site-lisp/debian-startup
/usr/share/emacs/24.2/site-lisp/dictionaries-common/flyspell hides 
/usr/share/emacs/24.2/lisp/textmodes/flyspell
/usr/share/emacs/24.2/site-lisp/dictionaries-common/ispell hides 
/usr/share/emacs/24.2/lisp/textmodes/ispell

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
easymenu 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 ielm pp comint regexp-opt ansi-color ring
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 font-render-setting
move-toolbar gtk x-toolkit x multi-tty emacs)