Made ia32/x64 code more uniform. Minor jump tweaks.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/20067003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15857 ce2b1a6d-e550-0410-aec6-3dcde31c8c00