More fixes in async machinery (issue 22438 and maybe more).

tests/language/regress_22438_test.dart

+// Copyright (c) 2015, 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 "dart:async";
+import "package:expect/expect.dart";
+
+main() async {
+  var error = "no error";
+  try {
+    try {
+      await new Future.error("error");
+    } on MissingType catch(e) {
+    }
+  } catch (e) {
+    error = e;
+  }
+  Expect.isTrue(error is TypeError);
+}