catch subclasses of Ouch as well

If something constructs a subclass of Ouch, it should still be caught by the subs in this module.

The main motivation for this change is that I have a module Carp::Always::WithObjects that forces all exceptions to have stack traces.  It does this by auto-subclassing any exception objects that get thrown.  This doesn't work for Ouch as is, because it checks the exact class name of the object instead of using isa.