nsf.c: - new function DependentSubClasses() to determine all classes that inherit from a given class. The result extend TransitiveSubClasses() by including class mixin relationships. - simplify NsfParameterCacheClassInvalidateCmd() by using the new function DependentSubClasses(). With the new implementation, NsfParameterCacheClassInvalidateCmd() is as efficient as before without to MostGeneralSuperclass optimization (but being complete now) when working on the root classes (an more efficient on subclasses).