Get basic superclass method calls working.

test/super/indirectly_inherited.wren

@@ -0,0 +1,18 @@
+class A {
+  foo {
+    io.write("A.foo")
+  }
+}
+
+class B is A {}
+
+class C is B {
+  foo {
+    io.write("C.foo")
+    super.foo
+  }
+}
+
+C.new.foo
+// expect: C.foo
+// expect: A.foo