Check multiple inheritance from subinterfaces

[lmove]

Check what happens with the following case (and others related to multiple inheritance of subinterfaces):

public interface I {
     int m();
}

public interface J extends I {
     int m();
}

public class C implements I, J {
     [...]
}

If in a newer version of the API we get:

public interface J extends I {
     default int m() {
          return 0;
     }
}

Add tests and needed tweaks.

Affected changes: methodNewDefault, methodAbstractNowDefault