Fixed constant folding in HMod.

We have to check for overflow before attempting to do a modulo operation,
otherwise Crankshaft itself segfaults on some platforms, e.g. ia32. Added tests
even for division, where the problem doesn't show up, just to be sure...

R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/14617014

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14629 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Elide hole checks on KeyedLoads of holey double arrays

Improves NavierStokes by about 5%

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/15014020

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14630 ce2b1a6d-e550-0410-aec6-3dcde31c8c00