Report compile-time errors for conflicting overrides as specified by latest

tests/language/setter_override2_test.dart

Index: tests/language/setter_override2_test.dart
===================================================================
--- tests/language/setter_override2_test.dart	(revision 0)
+++ tests/language/setter_override2_test.dart	(revision 0)
@@ -0,0 +1,27 @@
+// Copyright (c) 2013, 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.
+
+// Test that we do not report a compile-time error when an instance setter named
+// foo= is declared in a class inheriting an instance method, field, or getter
+// named foo, or an instance setter named foo=.
+
+import "package:expect/expect.dart";
+
+class A {
+  var foo = 42;  /// 00: ok
+  get foo => 42;  /// 01: ok
+  foo() => 42;  /// 02: ok
+  set foo(value) { }  /// 03: ok
+}
+
+class B extends A {
+  var foo_;
+  set foo(value) { foo_ = value; }
+}
+
+main() {
+  var b = new B();
+  b.foo = 42;
+  Expect.equals(42, b.foo_);
+}