checks mechanism != NULL, or NULL + non-empty zap_domain

Fix V815 Decreased performance. Consider replacing the expression 'options.socks_proxy_address != ""' with '!options.socks_proxy_address.empty()'. session_base.cpp 497

This is still raw and experimental.
To connect through a SOCKS proxy, set ZMQ_SOCKS_PROXY socket option on
socket before issuing a connect call, e.g.:

    zmq_setsockopt (s, ZMQ_SOCKS_PROXY,
        "127.0.0.1:22222", strlen ("127.0.0.1:22222"));
    zmq_connect (s, "tcp://127.0.0.1:5555");

Known limitations:
- only SOCKS version 5 supported
- authentication not supported
- new option is still undocumented

This bug is caused by fq which can terminate pipe before sending all
frames of a message first. So sometimes two messages were mixed and this
confused ZAP handler.

This patch just modifies one pipe parameter so that socket consumes all
messages before dropping the pipe.

This patch allows client applications to retrieve the remote endpoint from a message that originated from a tcp socket

As TIPC transport for 0MQ will only work on post 3.8
Linux kernels where nonblocking connect was added,
we add AC_RUN test to check for this functionality.
Should the test fail, tipc is excluded from build/test.
Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>

A ZeroMQ application can opt for TIPC based sockets
using the TIPC port name format:
zmq_bind(sb, "tipc://{type,lower,upper}");
zmq_connect(sc, "tipc://{type,inst}");

'type' is the service ID, and 'lower/upper' can be
used for service partitioning or basic load
balancing.

ZeroMQ TIPC transport requires a kernel >= 3.8
(nonblocking connect support for TIPC).
Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>

These were exposed to users, but have subsequently been removed as
sockopts. They are currently only being used by ZAP, so I've moved it to
a simpl function call (actually it's only used in one case even in that,
so there may be a further simplification possible there).

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.

- designed for TCP clients and servers
- added HTTP client / server example in tests/test_stream.cpp
- same as ZMQ_ROUTER + ZMQ_ROUTER_RAW + ZMQ_ROUTER_MANDATORY
- includes b893ce set ZMQ_IDENTITY on outgoing connect
- deprecates ZMQ_ROUTER_RAW

Copyrights had become ads for Sustrik's corporate sponsors, going against the original
agreement to share copyrights with the community (that agreement was: one line stating
iMatix copyright + one reference to AUTHORS file). The proliferation of corporate ads
is also unfair to the many individual authors. I've removed ALL corporate title from
the source files so the copyright statements can now be centralized in AUTHORS and
source files can be properly updated on an annual basis.

Zeromq shall never send/receive socket identifiers for sockets in raw
mode. The existing implementation breaks this requirement after
reconnection.

- add unlikely hints
- drop unnecessary assertion
- style fixes

There is no need to require the 'more' flag in the provided message
structure be 0 when pulling message from the session.

    - Created a new option ZMQ_ROUTER_RAW_SOCK
    - Added new raw_encoder and raw_decoder to receive and send messages in raw form to remote client
    - Added test case file tests/test_raw_sock.cpp

    o To create a raw router sock set the ZMQ_ROUTER_RAW_SOCK option
    o ZMQ_MSGMORE flag is ignored for non-id messages
    o To terminate a remote connection send id message followed by zero length data message

Ref: https://zeromq.jira.com/browse/LIBZMQ-417

Significantly reworked the monitoring infrastructure with a more granular per socket API and to play well with monitoring endpoints in application threads