Fix bugs in Scheduler hoisting and RPO loop bounds computations.

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/677683002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24877 ce2b1a6d-e550-0410-aec6-3dcde31c8c00