public interface ReferenceUnique
ReferenceUnique is a property indicating that, for
all instances of a class, (a==b)==(a.equals(b)).
That is, two equal objects are always reference equal.
Tagging classes with ReferenceUnique allows
automated checkers to more accurately discrimate legitimate
uses of == on objects from unsafe uses.
Copyright (c) 2006 C. Scott Ananian