The overflow conditions were not correctly detected for 
certain add, sub and mul instructions.

I replaced the previous code by using 64-bit arithmetic
to correctly identify overflows for *, + and -.

Review URL: http://codereview.chromium.org/5860009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6055 ce2b1a6d-e550-0410-aec6-3dcde31c8c00