Re-apply "Implement operator== and hashCode for bound closures."

tests/language/static_closure_identical_test.dart

+// 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.
+
+import "package:expect/expect.dart";
+
+var foo = main;
+
+main() {
+  Expect.equals(main, main);
+  Expect.identical(main, main);
+  Expect.equals(main.hashCode, main.hashCode);
+
+  Expect.equals(main, foo);
+  Expect.identical(main, foo);
+  Expect.equals(main.hashCode, foo.hashCode);
+}