Tests for issue #6152 added

Author: anatoliykmetyuk

tests/pos-special/i6152/A_1.java

@@ -0,0 +1,8 @@
+abstract class A_1 {
+  public abstract Object f();
+
+  public static abstract class B extends A_1 {
+    @Override
+    public abstract String f();
+  }
+}

tests/pos-special/i6152/B_2.scala

@@ -0,0 +1,3 @@
+class C extends A_1.B {
+  def f() = "hello"
+}