Add ROUTER socket option to introduce self(send an empty message) to new peers, to allow ROUTER<->ROUTER auto-discovery problem.

Add ROUTER socket option to introduce self(send an empty message) to new peers, to allow ROUTER<->ROUTER auto-discovery problem.

Working on Travis builds

- made consistent with options.cpp code
- added trace print for ongoing issue with Travis CI builds

Adding support for Travis CI

stdint.h isn't available on all platforms

Added as_server to options

- we need to switch to PLAIN according to options.mechanism
- we need to catch case when both peers are as-server (or neither is)
- and to use username/password from options, for client

Use socket options to select security mechanism

Added options 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

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.

Some changes to building and packaging

Implement ZMTP/3.0 NULL mechanism

zmq_msg_close clarification in man pages

Experimental function zmq_recviov doesnt work correctly in a couple of c...

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.

Fix return code redeclaration for platforms with SO_NOSIGPIPE

Fixed issue LIBZMQ-526