Give an error when setting break points in functions either defined through the API or in functions which are part of the V8 builtins.

BUG=178
Review URL: http://codereview.chromium.org/13785

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@977 ce2b1a6d-e550-0410-aec6-3dcde31c8c00