message: Construct an endpoint with a non-zero backlog length for listen().
  Matches a change in the dev branch of websocketpp.
diff: @@ -91,7 +91,7 @@ public:
  explicit endpoint()
  : m_io_service(NULL)
  , m_external_io_service(false)
  - , m_listen_backlog(0)
  + , m_listen_backlog(lib::asio::socket_base::max_connections)
  , m_reuse_addr(false)
  , m_state(UNINITIALIZED)
  {
  