javac fails to reject the following code, which has an ambiguity according
the the Java Language Specification, second edition.


// narrowed down from jacks 15.12.2.2-ambiguous-18

class A {
    protected void m(Object o, String s) {}
}
interface B {
    void m(String s, Object o);
}
abstract class C extends A implements B {}
abstract class D extends C {
    void foo() {
        super.m("", ""); // ambiguous!
    }
}