* Trace($boolean)
           Each "Exception::Class::Base" subclass can be set
           individually to include a a stracktrace when the
           "as_string" method is called.  The default is to not
           include a stacktrace.  Calling this method with a
           value changes this behavior.  It always returns the
           current value (after any change is applied).

           This value is inherited by any subclasses.  However,
           if this value is set for a subclass, it will there-
           after be independent of the value in "Excep-
           tion::Class::Base".

           This is a class method, not an object method.