start to implement unimplemented builtins, but only throw the NotImplemented error.  This is better than a NameError.
Add all unimplemented builtin functions to builtindict, and give them a simple implementation in builtins that just throws an exception.  This is better than NameError.
Merge branch 'refs/heads/builtin-cleanup'
Add placeholders for all unimplemented builtin functions.  Have the stub simply throw a NotImplemented exception.