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

tests/debugger/break_after_spawn_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.
 
 // Test that we get a meaningful list of processes.
 
-// DartinoDebuggerCommands=b resume,r,c
+// DartinoDebuggerCommands=b resume,r,c,q
 
 import 'dart:dartino';
 
 Port spawnPaused(Channel channel) {
   var port = new Port(channel);
   Process.spawnDetached(() {
     var c = new Channel();
     port.send(new Port(c));
     c.receive();
   });
   return channel.receive();
 }
 
 void resume(Channel channel, Port port) {
   port.send(null);
 }
 
 main() {
   Channel channel = new Channel();
   Port p = spawnPaused(channel);
   resume(channel, p);
 }