Finds and loads all classes that derive from a given set of super classes.
param
rootPackage Root package of classes to find. Use an empty string to find everyting.
param
superClasses The super classes of all the classes to find.
return
An hash map which keys are the super classes looked for and which values are
ArrayList of the classes found. The array lists are always created for all the
valid keys, they are simply empty if no deriving class is found for a given
super class.
Returns a string indicating the source of the classes, typically for debugging
or in error messages. This would typically be a JAR file name or some kind of
identifier that would mean something to the user when looking at error messages.
return
An informal string representing the source of the classes.
