Don't quit debugger when the program terminates, only after `quit`.

tests/debugger/unused_optional_test.dart

 // Copyright (c) 2016, the Dartino 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.md file.
 
-// DartinoDebuggerCommands=b main,r,s,s,l,c
+// DartinoDebuggerCommands=b main,r,s,s,l,c,q
 
 import 'package:expect/expect.dart';
 
 main() {
   // The default value for third parameter is evaluated in another file.
   // Ensure that the debug-info for default values is recorded correctly.
   Expect.equals(1, 1);
 }