Prototypes and their properties and methods are locked down to prevent fiddling with their operation, even if the build-in object leaks.

Made some built-in functions only work during bootstrapping.

Review URL: http://codereview.chromium.org/7799027

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9122 ce2b1a6d-e550-0410-aec6-3dcde31c8c00