Experimental function zmq_recviov doesnt work correctly in a couple of cases
1) VSM - you cannot hand out the 'data' address as it was not allocated on the heap
2) for other messages the 'data' address cannot be handed out either, as it not the address
originally returned by malloc and hence cannot be passed to 'free'.
see msg.cpp
u.lmsg.content = (content_t*) malloc (sizeof (content_t) + size_);
....
u.lmsg.content->data = u.lmsg.content + 1;

So the function is changed to always malloc a data buffer and copy the data into it.
There is a possible optimisation using memmove for the non-VSM case but that is not done yet.
Merge pull request #550 from JonDyte/iovec

Experimental function zmq_recviov doesnt work correctly in a couple of c...
Clarified zmq_msg_close not needed after zmq_msg_send
Fixed up test_iov case
Merge pull request #551 from hintjens/master

zmq_msg_close clarification in man pages
Implement ZMTP/3.0 NULL mechanism
Update test_raw_sock to work with ZMTP/3.0
Merge pull request #552 from hurtonm/master

Implement ZMTP/3.0 NULL mechanism
Added configure check for libsodium
Fixed packaging for Windows - was missing errno sources
Use correct libsodium call for detection
Merge pull request #553 from hintjens/master

Some changes to building and packaging
Abstract security mechanism
Implement ZMTP/3.0 PLAIN mechanism

This implements protocol handshake.
We still need to design and implement 1) API changes so a user
can set username and password, and 2) a mechanism for engine
to authenticate users.
Merge pull request #554 from hurtonm/master

Implement ZMTP/3.0 PLAIN mechanism
Fixed sizeof usage in man pages
Added configuration for PLAIN security

* ZMQ_PLAIN_SERVER, ZMQ_PLAIN_USERNAME, ZMQ_PLAIN_PASSWORD options
* Man page changes to zmq_setsockopt and zmq_getsockopt
* Man pages for ZMQ_NULL, ZMQ_PLAIN, and ZMQ_CURVE
* Test program test_security
Merge pull request #555 from hintjens/master

Added options for PLAIN security
Use socket options to select security mechanism
Merge pull request #556 from hurtonm/master

Use socket options to select security mechanism