safer version of UNIVERSAL::isa

 UNIVERSAL is base class for ALL classes in Object Oriented Perl.
 UNIVERSAL::isa (isa stands for "is a") is method which can tell
 You if object is blessed in package or inherits from package.
 .
 This module overloads UNIVERSAL::isa with a version that makes sure
 that, when called as a function on objects which override isa, isa will
 call the appropriate method on those objects
 .
 In all other cases, the real UNIVERSAL::isa gets called directly.