ActivationDesc and ActivationGroupDesc are used to specify the necessary
information to create an instance of a specific object or group respectively.
Currently, these descriptors use a CodeSource to indicate the location of
the class specified in the descriptor. A CodeSource is the wrong abstraction
to use for this purpose since it provides no extra verification that RMI
could do that isn't already done by the SecureClassLoader. Instead of
CodeSource, a URL should be used to indicate a class's location. A URL is
the only information needed to load the class.