frog await: allow errors after the await within try-catch blocks.

frog/tests/await/src/TryCatch8Test.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.
 
 // Await within a try-catch block, the awaited future produces the error, the
 // future is not normalized.
 
 #import("await_test_helper.dart");
 
 errorDuring() {
   try {
-    final t = await errorOf("my error");
+    final t = await errorOf("my error"); // needs normalization
     return t;
   } catch (e) {
     Expect.equals("my error", e);
     return 2;
   }
 }
 
 main() {
   int t = await errorDuring();
   Expect.equals(2, t);
 }