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

frog/tests/await/nested_try_catch4_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 within a nested try-catch block, throw happens on await, inner catch
 // has priority.
 
 #import("await_test_helper.dart");
 
 class E1 implements Exception {
   const E1([msg=null]);
 }
 
 awaitAndThrow(Exception ex) {
   try {
     try {
       final f = errorOf(ex);
       final t = await f;
       return 0;
     } catch (E1 e) {
       return 1;
     }
   } catch (E1 e) {
     return 2;
   }
 }
 
 main() {
   int t = await awaitAndThrow(const E1());
   Expect.equals(1, t);
 }