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

frog/tests/await/doubly_nested_function_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
+
 // Await in doubly-nested functions.
 
 #import("await_test_helper.dart");
 
 bool called = false;
 
 main() {
   f1() {
     f2() {
       final x = await futureOf(3);
       return x + 1;
     }
     final x = await f2();
     return x + 10;
   }
   final x = await f1();
   Expect.equals(14, x);
 }