activation group unable to load classes in classpath

An activation group is unable to load activatable objects located in
classpath. With the new changes to load the application classes via
the application URLClassLoader and to not locate classpath classes via
findSystemClass, classpath classes cannot be loaded. Since the activation
group implementation is found among the system classes, it will attempt
to load classes wrt a null classloader and classpath classes are no
longer found via the null classloader.