Skip the write barrier for global property cell writes. The heap

Skip the write barrier for global property cell writes.  The heap
verification code was refactored to avoid verifying that property
cells have correct remembered sets.

Review URL: http://codereview.chromium.org/149392

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2423 ce2b1a6d-e550-0410-aec6-3dcde31c8c00