Stop TThreadPoolServer with alive connections.

Now if client of TThreadPoolServer kept alive connection (for example if requests to thrift-server are forwarded from nginx-server, which is set up so that the connections between him and thift-server are kept alive), method TThreadPoolServer::stop does not stopped server. It continues work until client (nginx-server) will not stopped.

void StopThread(shared_ptr<EchoService> const &echo_service_handler,
				shared_ptr<TThreadPoolServer> &server,
				shared_ptr<ThreadManager> &thread_manager)
{
	while (echo_service_handler->GetRequestsCount() < 3)
	{
		sleep(1);
	}
	std::cout << "Stop service." << std::endl;
	server->stop();
}

I think that ability to stop thrift-server with alive connections will be useful.