Implement new equality spec.

tests/language/equality_test.dart

+// Copyright (c) 2012, 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.
+
+
+class A {
+  bool _result;
+  A(this._result);
+  operator ==(x) { return _result; }
+}
+
+
+opaque(x) => [x,1,'y'][0];  // confuse the optimizers.
+
+class Death {
+  operator ==(x) { throw 'Dead!'; }
+}
+
+death() => opaque(new Death());
+nullFn() => opaque(null);
+
+tests() {
+  var alwaysTrue = new A(true);
+  var alwaysFalse = new A(false);
+  Expect.isFalse(alwaysFalse == alwaysFalse);
+  Expect.isTrue(alwaysFalse != alwaysFalse);
+  Expect.isTrue(alwaysTrue == alwaysTrue);
+  Expect.isTrue(alwaysTrue == 5);
+  Expect.isFalse(alwaysTrue == null);
+  Expect.isFalse(null == alwaysTrue);
+  Expect.isTrue(alwaysTrue != null);
+  Expect.isTrue(null != alwaysTrue);
+  Expect.isTrue(null == null);
+  Expect.isFalse(null != null);
+  
+  Expect.throws(() => death() == 5);
+  Expect.isFalse(death() == nullFn());
+  Expect.isFalse(nullFn() == death());
+  Expect.isTrue(nullFn() == nullFn());
+  Expect.isTrue(death() != nullFn());
+  Expect.isTrue(nullFn() != death());
+  Expect.isFalse(nullFn() != nullFn());
+}
+
+main() {
+  for (int i = 0; i < 1000; i++) tests();
+}