Previously, HDiv never had its CanOverflow flag cleared and HMod had
inverted logic (compared to HAdd, HSub and HMul). Minor cleanups on the way.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/14617015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14644 ce2b1a6d-e550-0410-aec6-3dcde31c8c00