Code cleanup
Merge pull request #770 from hurtonm/master

Code cleanup
Updated documentation for zmq_disconnect() and zmq_setsockopt().
Intial IPC accept filter support.

Adds sets of process (Linux only), user, and group IDs for filtering
connections from peer processes over IPC transport.  If all of the
filter sets are empty, every connection is accepted.  Otherwise,
credentials for a connecting process are checked against the filter sets
and the connection is only accepted if a match is found.

This commit is part of LIBZMQ-568 and only adds the filter sets and
implements the filter in the IPC accept method.  The interface for
adding IDs to filter sets are included in a separate commit.

IPC accept filtering is supported only on Linux and OS X.
Add IPC accept filter socket options.

Adds ZMQ_IPC_ACCEPT_FILTER_{PID,UID,GID} socket options to add processs,
user, and group IDs to the IPC filter sets. Fixes LIBZMQ-568.
use enum retired_fd instead of -1

using -1 causes a warning on Windows platform because SOCKET is unsigned.
Merge pull request #773 from hashstat/master

Add IPC accept filter support
Merge pull request #774 from shubred1/master

Updated documentation for zmq_disconnect() and zmq_setsockopt().
Merge pull request #775 from pijyoi/master

use enum retired_fd instead of -1
add test_curve_proxying.cpp