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

tests/debugger/break_in_other_process_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 can break at a breakpoint hit by another process than main.
 
-// DartinoDebuggerCommands=b foo,r,bt,c
+// DartinoDebuggerCommands=b foo,r,bt,c,q
 
 import 'dart:dartino';
 import 'package:expect/expect.dart';
 
 int foo() => 42;
 
 other(Port port) {
   port.send(foo());
 }
 
 main() {
   var channel = new Channel();
   var port = new Port(channel);
   Process.spawnDetached(() { other(port); });
   Expect.equals(42, channel.receive());
 }