converting the operands to 32-bit ints directly in the 
machine code stub instead of just checking if the heap 
numbers really just represent 32-bit ints and going
through the runtime system in that case.
Review URL: http://codereview.chromium.org/21536

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1330 ce2b1a6d-e550-0410-aec6-3dcde31c8c00