message: Trace-log at least part of actor_system's dtor
diff: @@ -291,6 +291,8 @@ actor_system::actor_system(actor_system_config& cfg)
  }
  actor_system::~actor_system() {
  + {
  + CAF_LOG_TRACE("");
  CAF_LOG_DEBUG("shutdown actor system");
  if (await_actors_before_shutdown_)
  await_all_actors_done();
  @@ -310,6 +312,7 @@ actor_system::~actor_system() {
  (*i)->stop();
  await_detached_threads();
  registry_.stop();
  + }
  // reset logger and wait until dtor was called
  CAF_SET_LOGGER_SYS(nullptr);
  logger_.reset();
  