Add --version option to dart2js and add version information (if available) to generated code.

sdk/bin/dart2js

 #!/bin/bash
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 function follow_links() {
   while [ -h "$1" ]; do
     # On Mac OS, readlink -f doesn't work.
     1="$(readlink "$1")"
   done
@@ skipping 23 matching lines @@
   if test 8 -le `tput colors`; then
     # Stdout has at least 8 colors, so enable colors.
     EXTRA_OPTIONS[${#EXTRA_OPTIONS[@]}]='--enable-diagnostic-colors'
   fi
 fi
 
 unset EXTRA_VM_OPTIONS
 declare -a EXTRA_VM_OPTIONS
 
 if test -f "$SNAPSHOT"; then
-  # TODO(ahe): Remove the following line when we are relatively sure it works.
-  echo Using snapshot "$SNAPSHOT" 1>&2
-
   EXTRA_OPTIONS[${#EXTRA_OPTIONS[@]}]="--library-root=$SDK_DIR"
 fi
 
 # Tell the VM to grow the heap more aggressively. This should only
 # be necessary temporarily until the VM is better at detecting how
 # applications use memory.
 # TODO(ahe): Remove this option (http://dartbug.com/6495).
 EXTRA_VM_OPTIONS[${#EXTRA_VM_OPTIONS[@]}]='--heap_growth_rate=512'
 
 case $0 in
   *_developer)
     EXTRA_VM_OPTIONS[${#EXTRA_VM_OPTIONS[@]}]='--checked'
     ;;
 esac
 
 if test -f "$SNAPSHOT"; then
   exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "dart2js" \
       "${EXTRA_OPTIONS[@]}" "$@"
 else
   exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "$DART2JS" "${EXTRA_OPTIONS[@]}" "$@"
 fi