to get rid of global object loaded from a snapshot. This
eliminates the "double global object" issue. Thanks to Mads
for suggesting this!

Review URL: http://codereview.chromium.org/2865013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4917 ce2b1a6d-e550-0410-aec6-3dcde31c8c00