Adding Smi support to Add, Sub, Mul, and Bitwise

R=svenpanne@chromium.org

Review URL: https://chromiumcodereview.appspot.com/20070005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15879 ce2b1a6d-e550-0410-aec6-3dcde31c8c00