Update zmq::multipart_t::send to support zmq::send_flags

[cacharle]

cppzmq/zmq_addon.hpp

Line 474 in 3bcbd9d

bool send(socket_ref socket, int flags = 0)

zmq::multipart_t::send still uses the old int send flags.

[cacharle]

Well, after looking at the deprecated crazyness in socket_t::send, I'm not sure how to tackle this..