Add windows scripts equivalent to the macos/linux scripts in sdk/bin.

sdk/bin/pub.bat

Index: sdk/bin/pub.bat
===================================================================
--- sdk/bin/pub.bat	(revision 0)
+++ sdk/bin/pub.bat	(revision 0)
@@ -0,0 +1,17 @@
+@echo off
+REM Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+REM for details. All rights reserved. Use of this source code is governed by a
+REM BSD-style license that can be found in the LICENSE file.
+
+REM Run pub.dart on the Dart VM. This script assumes the Dart SDK's directory
+REM structure.
+
+set SCRIPTPATH=%~dp0
+
+REM Does the string have a trailing slash? If so, remove it.
+if %SCRIPTPATH:~-1%==\ set SCRIPTPATH=%SCRIPTPATH:~0,-1%
+
+REM Set DART_SDK so pub can find SDK packages.
+set DART_SDK=%SCRIPTPATH%\..\
+
+"%SCRIPTPATH%\dart" "%SCRIPTPATH%\..\util\pub\pub.dart" %*