Warn when calling an overridden contract method - most likely missing the target reference

[BenRomberg]

Example - assert getX() should really be assert target.getX():

public class A {

    private int x;

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

}

import static de.andrena.c4j.Condition.postCondition;
import static de.andrena.c4j.Condition.preCondition;
import de.andrena.c4j.Target;

public class AContract extends A {

    @Override
    public void setX(int x) {
        if (preCondition()) {
            assert x > 0 : "x > 0";
        }
        if (postCondition()) {
            assert getX() == x : "x set";
        }
    }

}

import org.junit.Test;

public class ATest {

    @Test
    public void test() {
        A a = new A();
        a.setX(5);
    }

}