cappython

Add add_module() method to ModuleLoader

Block assignments to self.__class__, because that allows an object to change its type

Handle and reject "exec" statements so that running the verifier on safeeval.py gives a nicely-formatted error message instead of raising AssertionError

Disallow use of __metaclass__, which would allow method functions to escape

Make the __builtins__ object a module rather than a dict so that it is read-only to CapPython code