Implemented zmq_send_const
Added zmq_send_const test
Fix doc typo
Add #include to string.h in blob.hpp

Required for memmove(), memcpy()
Add try_lock() to mutex_t
Add scoped_lock_t syntactic sugar
Declare ZMQ_CONFLATE option
Implement double buffer for conflate option

Add simple double buffer implementation tailored to handle msg_t,
i.e invoke msg_t::close instead of destructor and so on.
Seems to me mutex is good enough at this point.
Plug in dbuffer to serve the ZMQ_CONFLATE option

ZMQ_CONFLATE option is passed to pipepair() which creates a usual
ypipe_t or ypipe_conflate_t and plugs it into pipe_t under a common
abstract base.
Update doc for ZMQ_CONFLATE socket option
Merge pull request #625 from ulikoehler/zmq_send_const

Add zmq_send_const for constant data
Attempt to fix disconnect not respecting linger

Looks like linger is honoured properly, but shutting down the session
causes the pipe termination to come from that side - because the local
pipe then shuts down right away it seems to trigger a terminated on the
other end instead of waiting. This way we trigger the termination from
the local end and then terminate the session.
Merge pull request #624 from ricnewton/master

Port tests to windows and add to cmake build.
Merge pull request #627 from ianbarber/master

Attempt to fix disconnect not respecting linger
Added message type for constant messages
Fix indentation
Merge pull request #630 from ulikoehler/cmsg

Optimized zmq::msg_t for constant messages
Minor fixes to doc ; added zmq_msg_init_data() assert preventing deferred segfault
Add test for ZMQ_CONFLATE option
Fix spaces before comments