superclass? and subclass? assuming OWLClass returned

The isuperclasses and isubclasses methods return all
classes which includes any OWLClassExpressions, rather than just
named OWLClass. While we need to check the former, only the latter
can be recursed down (without reasoning).
Fixed isuperclasses.

Missed second argument of instance? And yet, clojure does not
pick this up with an arity error. Not for the first time.