bug#8632: 23.2; shell-script[bash] doesn't handle bitshift $(( 1 << 16 ))

[Ben Wong <bug-gnu-emacs+gnu.org@wongs.net>]

In shell-script mode (bash minor mode) Emacs 23.2 incorrectly parses the
following line as a HERE DOCUMENT.

	echo $(( 1 << 16 ))

It is confused because sh-font-lock-open-heredoc (in sh-script.el)
does not know about bash's ARITHMETIC EXPANSION. There should be a
function, similar to sh-in-comment-or-string, which parses the
script looking for arithmetic expansion.

As a temporary workaround for users, I believe it is legal to put double
quotes around any arithmetic expansion to force emacs to view it as a
string.


In GNU Emacs 23.2.1 (i486-pc-linux-gnu, GTK+ Version 2.20.0)
 of 2010-12-11 on raven, modified by Debian
configured using `configure  '--build' 'i486-linux-gnu' '--build' 'i486-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/emacs23:/etc/emacs:/usr/local/share/emacs/23.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.2/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.2/leim' '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 'build_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

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: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Shell-script

Minor modes in effect:
  shell-dirtrack-mode: t
  gpm-mouse-mode: t
  which-function-mode: t
  show-paren-mode: t
  display-time-mode: t
  recentf-mode: t
  iswitchb-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  size-indication-mode: t
  line-number-mode: t