Marsaglia's multiply-with-carry instead of mixing the
bits obtained from calling the system random() twice.

This seems to be a bit faster and gives a better 
distribution than the system random() in particular on 
Windows. 
Review URL: http://codereview.chromium.org/126113

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2159 ce2b1a6d-e550-0410-aec6-3dcde31c8c00