Separate Cell and PropertyCell spaces

This makes it possible to store additional information on property cells, for example Type and optimized Code dependencies.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/16631002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15089 ce2b1a6d-e550-0410-aec6-3dcde31c8c00