Add X87 implementations for Integer32ToDouble, DoubleToI, DoubleToSmi

Additionally refactor the X87Stack tracking

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/20781007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16246 ce2b1a6d-e550-0410-aec6-3dcde31c8c00