Fixed setting TCP keepalive parameters on Windows

Fixes to IPC wildcarding & test cases

- was not waiting long enough at socket close
- increased to 50 msec

Fixed use of deprecated tempnam

add failing test for binding to resources

Update doc for zmq_proxy_steerable [ci skip]

Add tests/test_zap_ipc_creds to .gitignore

Single connect

support signaler_port in config.hpp set to value other than 0 and 5905

tools/: Link curve_keygen with a c++ linker

When trying to linking curve_keygen as if it was a C program, linking
fails (at least with gcc 4.8 on Debian testing) because it can't find
C++ symbols. Linking with g++ instead fixes the issue.

To achieve this, the source is renamed to curve_keygen.cpp, and
tools/Makefile.am is updated accordingly.
Signed-off-by: Gergely Nagy <algernon@balabit.hu>

Add support for extending ZAP request address with IPC peer credentials.

Another take on LIBZMQ-568 to allow filtering IPC connections, this time
using ZAP.  This change is backward compatible.  If the
ZMQ_ZAP_IPC_CREDS option is set, the user, group, and process IDs of the
peer process are appended to the address (separated by colons) of a ZAP
request; otherwise, nothing changes.  See LIBZMQ-568 and zmq_setsockopt
documentation for more information.

Enable building IPC filtering with cmake and another small autoconf fix.

Shortened ZMQ_IPC_ACCEPT_FILTER_[UGP]ID to ZMQ_IPC_FILTER_[UGP]ID.

Fix failing test case in test_filter_ipc.

Add explicit check for primary group.

use enum retired_fd instead of -1

Updated documentation for zmq_disconnect() and zmq_setsockopt().

Add IPC accept filter support

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

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.

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.