Addded an option (default disabled) to enable tcp keepalive

                  'write': select.POLLOUT, 'hup': select.POLLHUP,

                  'error': select.POLLERR | select.POLLNVAL}

    def __init__(self, sock, loop=None, *args, **kwargs):

    def __init__(self, sock, loop=None, enable_tcp_keepalive=False,

                 *args, **kwargs):

        # Sock of this connection:

        self._sock = sock

        sock.setblocking(False)

            self.loop = loop

        # Activate TCP keepalive on the connection:

        #self._sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)

        if enable_tcp_keepalive:

            self._sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)

        # Watcher list:

        self._watchers = set()