Added tests for interfaces that extend other interfaces.

Exercises IsAssignableFrom and FindInterfaceMethod. Also made
Class::Implements private again and switched to using IsAssignableFrom.

Change-Id: Iea195a2cc124a87ebb3d87d778a7edcd25984b46
diff --git a/test/Interfaces/Interfaces.java b/test/Interfaces/Interfaces.java
index 0b72e92..4bd9bfe 100644
--- a/test/Interfaces/Interfaces.java
+++ b/test/Interfaces/Interfaces.java
@@ -8,9 +8,17 @@
         public void j1();
         public void j2();
     }
+    interface K extends J {
+        public void k();
+    }
     class A implements I, J {
         public void i() {};
         public void j1() {};
         public void j2() {};
     }
+    class B implements K {
+        public void j1() {};
+        public void j2() {};
+        public void k() {};
+    }
 }