Revert "Simplify v8/Isolate teardown."

This reverts commit r20876, it broke non-snapshot tests.

TBR=bmeurer@chromium.org

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20879 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Optimize numeric comparison with known successors.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/246133005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20880 ce2b1a6d-e550-0410-aec6-3dcde31c8c00