The check whether a 32-bit signed integer is in the Smi
range is now Sign bit( value + 0x40000000 ) == 0,
done with a single cmp instruction.
Review URL: http://codereview.chromium.org/18710

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1134 ce2b1a6d-e550-0410-aec6-3dcde31c8c00