This avoid unwanted sharing between different function prototypes and in
general should help inlining because constant function properties on one
prototype don't affect other prototypes anymore.

BUG=v8:1716
Review URL: http://codereview.chromium.org/7994001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9393 ce2b1a6d-e550-0410-aec6-3dcde31c8c00