GCs (not just mark-compacts) and make the mark-compact
shortcutting of cons-strings identical to the scavenge
version.
Review URL: http://codereview.chromium.org/67125

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1699 ce2b1a6d-e550-0410-aec6-3dcde31c8c00