Update zeromq to 4.0.4.

0MQ version 4.0.4 stable, released on 2014/03/10
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Bug Fixes
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* Fixed #909; out of tree build issue on Linux.

* Fixed #888; hangs on terminate when inproc connected but never bound.

* Fixed #868; assertion failure at ip.cpp:137 when using port scanner.

* Fixed #818; fix timestamp counter on s390/s390x.

* Fixed #817; only export zmq_* symbols.

* Fixed #797; fixed setting TCP keepalive on Windows.

* Fixed #775; compile error on Windows.

* Fixed #763; when talking to a ZMTP v1 peer (libzmq 2.2), a socket would
  send an extra identity frame at the start of the connection.

* Fixed LIBZMQ-576 - Crash closing a socket after zmq_msg_send returns
  EAGAIN (reverts LIBZMQ-497)

* Fixed LIBZMQ-584; subscription filters getting lost on reconnection.
Updated net/zeromq to 4.0.4
fixes for old bmake, undefined variable is not treated as empty.