Fixed hash code computation on ia32 and x64 to match the runtime
system (change arithmetic shift right to logical shift right).

Review URL: http://codereview.chromium.org/2731007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4843 ce2b1a6d-e550-0410-aec6-3dcde31c8c00