Fix a problem with gclient not being able to download tools such as svn.

It turns out that Shell.Application.NameSpace works with relative paths 
on some systems only.  This failed on my Windows 7 box.


Review URL: http://codereview.chromium.org/115184

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@15754 0039d316-1c4b-4281-b951-d872f2087c98

bootstrap/win/win_tools.bat

@@ -10,7 +10,11 @@
 :: returned.
 
 set WIN_TOOLS_ROOT_URL=http://src.chromium.org/svn/trunk/tools
-set WIN_TOOLS_ROOT_DIR=%~dp0..\..
+
+:: Get absolute root directory (.js scripts don't handle relative paths well).
+pushd %~dp0..\..
+set WIN_TOOLS_ROOT_DIR=%CD%
+popd
 
 if "%1" == "force" (
   set WIN_TOOLS_FORCE=1