Make qldoc clearer about behaviour of override

[owen-mc]

The example that prompted this change was e.getTarget().hasQualifiedName("a","b"), where e is a CallExpr. Because the result of getTarget is a Function and the override is on its subclass Method, the documentation for the override on Method is not readily available. Since the behaviour is quite different for Method, we note it in the documentation of the original predicate.