Fixed global object leak caused by overwriting the global receiver (the global proxy) in the global object with the global object itself.

This CL additionally removes the API function to reattach a global proxy to a
global object.

BUG=324812
LOG=y
R=dcarney@chromium.org, titzer@chromium.org

Review URL: https://chromiumcodereview.appspot.com/101733002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18299 ce2b1a6d-e550-0410-aec6-3dcde31c8c00