condition for while and for loops.

http://code.google.com/p/v8/issues/detail?id=260

Review URL: http://codereview.chromium.org/40294

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1453 ce2b1a6d-e550-0410-aec6-3dcde31c8c00