Add test for unbinding inproc socket.

Resolve issue #949

Windows: if WSA error number is held, use directly.

It must be done this way, as WSAGetLastError returns 0 in these circumstances

vs2012: Add missing socks files

Don't delay reception of signal

- new code may help undersdtand issue #1108
  (https://github.com/zeromq/libzmq/issues/1108)
- code cleanups

Fix to build on OpenBSD

Add static compilation on CMake

Thread scheduling parameters: Use ZMQ context options instead of environment variables.

environment variables.

Code cleanup

Problem: two header files for a single library

Add missing socks files

socks: fix build on FreeBSD

The fix should be sane on all UNIX-like systems, so there's
no ZMQ_HAVE_FREEBSD involved.  It's likely that other BSDs
stumble across this problem too.

Solution: fixed this. Also minor code cleanups.

Users who need e.g. zmq_curve_keypair() have to remember to include
zmq_utils.h, which is counter-intuitive. The whole library should be
represented by a single include file.

Solution: merge all contents of zmq_utils.h into zmq.h, and deprecate
zmq_utils.h. Existing apps can continue unchanged. New apps can ignore
zmq_utils.h completely.

Problem: zmq_msg_gets did not set errno on unknown properties

Solution: set errno to EINVAL when a property does not exist.

Also fixed test_metadata.cpp to test this case.

Reverted removal of [ ] support 

This reverts commit 78a7b469.

Set EINVAL on invalid tcp:// endpoint in zmq_connect

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

Allow change of pthread priority

Rationale: In a real-time environment it is sometime mandatory to tune
threads priority and scheduling policy. This is required by our users
who mixes real-time and server threads within
the same process. It's not planned to support this on non-pthread
platforms (e.g. Windows).

Problem: zmq_connect() does not validate TCP addresses

This syntax is undocumented and has no known meaning. It was in libzmq
since 3.x.

Solution: remove this code.