Abstract class detection fails with overloaded names

[nickbattle]

This is equivalent to Overture bug #366. When an abstract function or operation is inherited by a subclass, that class is also abstract (cannot be instantiated) unless it implements the op/fn. This works. However, if the subclass has another op/fn that would overload with the inherited name, it is still necessary to implement the abstract op/fn to allow instantiation, but this test does not work. The following specification allows B to be instantiated (but it is abstract):

class A
operations
    public op: () ==> ()
    op() == is subclass responsibility;
end A

class B is subclass of A
operations
    public op: nat ==> ()
    op(-) == skip;
end B

[nickbattle]

After the fix, the specification now regards B as abstract, stating the unimplemented operation:

> p new B()
Error 3330: Cannot instantiate abstract class B in 'A' (console) at line 1:1
Unimplemented: op(() ==> ())