lingering step 2 of the test rename overhaul: make await tests also a directory

frog/tests/await/single_await2_test.dart

 // Copyright (c) 2011, 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.
 
+// The next line is used to tell test.dart that this test is run by invoking
+// awaitc.dart and passing this file as an argument (e.g. frog
+// frog/await/awaitc.dart test.dart):
+// VMOptions=frog/await/awaitc.dart
+
 // Linear await with the minimal required normalization in the code.
 #import("await_test_helper.dart");
 
 main() {
   final x = await futureOf(3);
   Expect.equals(3, x);
 }