This is a fix and reapply of r8516 with some comments addressed and more
tests added.
The difference from r8516 is that canonicalization of number literals is
no performed using the same methods as in v8, to avoid false positives/negatives
when detecting duplicates.

Review URL: http://codereview.chromium.org/7193045

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8541 ce2b1a6d-e550-0410-aec6-3dcde31c8c00