Solution: set errno to EINVAL when tcp:// endpoint is invalid (was just
leaving errno to previous value).

Since https://github.com/zeromq/libzmq/commit/350a1a, TCP addresses
get resolved asynchronously, so zmq_connect no longer returned an
error on incorrect addresses.

This is troublesome since we rely on some error checking to catch
blatant errors.

Solution add some upfront syntax checking that catches at least the
obvious kinds of errors (invalid characters, wrong or missing port
number).

- limit visibility of pending_connection_t
- add const qualifiers

- add const modifier to address parameter of event generating functions

Specifically:

* zmq_event_t should not be used internally in libzmq, it was
  meant to be an outward facing structure.

* In 4.x, zmq_event_t does not correspond to monitor events, so
  I removed the structure entirely.

* man page for zmq_socket_monitor is incomplete and the example
  code was particularly nasty.

* test_monitor.cpp needed rewriting, it was not clean.

This reverts commit 79b81f48.
Was causing:

Assertion failed: destroyed (socket_base.cpp:154)
/bin/bash: line 5: 31344 Aborted                 ${dir}$tst
FAIL: test_many_sockets

On TravisCI.

  V547 Expression 'file_desc >= 0' is always true. Unsigned type value is always >= 0. socket_base.cpp 845
  V547 Expression 'file_desc >= 0' is always true. Unsigned type value is always >= 0. socket_base.cpp 863
  V547 Expression 'file_desc >= 0' is always true. Unsigned type value is always >= 0. socket_base.cpp 897
  http://www.viva64.com/en/d/0137/print/

This reverts commit 50d34e56.

Fixes #872

Delete the socket if the initialization part of the socket creation
fails.

Call the allocation assertion macro before dereferencing the socket
pointer.

The get_credential () member function returns
credential for the last peer we received message for.
The idea is that this function is used to implement user-level API.

Also moved the fd field from message content to message itself

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

using -1 causes a warning on Windows platform because SOCKET is unsigned.

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>

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>

icanhasall is cute (for now), but the effect of the variable is clear
only after tracking down its origin reading the commit. This change is
intended to make it easier for people to have some intuition about its
effect from its name.

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).

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.

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.