Log Message:
Update zeromq to 2.1.7.

0MQ version 2.1.7 (Stable), released on 2011/05/12
==================================================

Bug fixes
---------

* Fixed issue 191, message atomicity issue with PUB sockets (an old issue).

* Fixed issue 199 (affected ROUTER/XREP sockets, an old issue).

* Fixed issue 206, assertion failure in zmq.cpp:223, affected all sockets
  (bug was introduced in 2.1.6 as part of message validity checking).

* Fixed issue 211, REP socket asserted if sent malformed envelope (old issue
  due to abuse of assertions for error checking).

* Fixed issue 212, reconnect failing after resume from sleep on Windows
  (due to not handling WSAENETDOWN).

* Properly handle WSAENETUNREACH on Windows (e.g. if client connects
  before server binds).

Changes
-------

* Runtime checking of socket and context validity, to catch e.g. using a
  socket after closing it, or passing an invalid pointer to context/socket
  methods.

* Test cases moved off port 5555, which conflicts with other services.

* Clarified zmq_poll man page that the resolution of the timeout is 1msec.