Fix various inheritance bugs

tests/language/override_field_method6_negative_test.dart

Index: tests/language/override_field_method6_negative_test.dart
===================================================================
--- tests/language/override_field_method6_negative_test.dart	(revision 14582)
+++ tests/language/override_field_method6_negative_test.dart	(working copy)
@@ -1,22 +0,0 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-// Dart test error for overriding method with setter.
-
-class A {
-  foo(x) { }
-}
-
-class B extends A {
-  set foo(x) { }  // setter cannot override method.
-}
-
-class OverrideFieldMethod6NegativeTest {
-  static testMain() {
-    new B().foo = 10;
-  }
-}
-
-main() {
-  OverrideFieldMethod6NegativeTest.testMain();
-}