Fix null.runtimeType, reflect(null).type.superinterfaces, and reflect(null).getField.

tests/language/null2_test.dart

+// Copyright (c) 2014, 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.
+// Second dart test program.
+
+import "package:expect/expect.dart";
+
+// Magic incantation to avoid the compiler recognizing the constant values
+// at compile time. If the result is computed at compile time, the dynamic code
+// will not be tested.
+confuse(x) {
+  try {
+    if (new DateTime.now().millisecondsSinceEpoch == 42) x = 42;
+    throw [x];
+  } on dynamic catch (e) { return e[0]; }
+  return 42;
+}
+
+main() {
+  Expect.equals("Null", null.runtimeType.toString());
+  Expect.equals("Null", confuse(null).runtimeType.toString());
+}