Problem: ZMQ_TCP_RETRANSMIT_TIMEOUT is a clumsy name

Solution: rename to ZMQ_MAXRT

This is the option name used on Windows, so easier to use and
remember.

src/tcp_connecter.cpp

@@ -146,7 +146,7 @@ void zmq::tcp_connecter_t::out_event ()
 
     tune_tcp_socket (fd);
     tune_tcp_keepalives (fd, options.tcp_keepalive, options.tcp_keepalive_cnt, options.tcp_keepalive_idle, options.tcp_keepalive_intvl);
-    tune_tcp_retransmit_timeout (fd, options.tcp_retransmit_timeout);
+    tune_tcp_maxrt (fd, options.tcp_maxrt);
 
     // remember our fd for ZMQ_SRCFD in messages
     socket->set_fd (fd);