This avoids creating a new map for every bound function. Bonus: some cleanup in Runtime_FunctionBindArguments.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/335653002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21839 ce2b1a6d-e550-0410-aec6-3dcde31c8c00