Solution: check for availability in CMake and autoconf before using it

Linux now supports Virtual Routing and Forwarding (VRF) as per:

https://www.kernel.org/doc/Documentation/networking/vrf.txt

In order for an application to bind or connect to a socket with an
address in a VRF, they need to first bind the socket to the VRF device:

    setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, dev, strlen(dev)+1);

Note "dev" is the VRF device, eg. VRF "blue", rather than an interface
enslaved to the VRF.

Add a new socket option, ZMQ_BINDTODEVICE, to bind a socket to a device.
In general, if a socket is bound to a device, eg. an interface, only
packets received from that particular device are processed by the socket.

If device is a VRF device, then subsequent binds/connects to that socket
use addresses in the VRF routing table.

Gyp needs its own platform.hpp; there is no way to delete this
file automatically.

Solution: copy gyp's platform.hpp into src, so that things build
properly no matter what the starting state. If you build with gyp
and then try to build using autotools' makefile, you'll get an
error from the platform.hpp.

This is rather insane since the code knows well enough what systems
support if_nametoindex. I blame this on over-use of autotools early
in libzmq's days.

Anyhow, this breaks gyp builds on OS/X.

Solution: add ZMQ_HAVE_IFADDRS to build/gyp/platform.hpp for OS/X.

Solution: add necessary macros into builds/gyp/platform.hpp

Work for Linux now, other platforms to test.

I'm adding gyp support so that we can easily pull in libzmq
and other C/C++ projects into gyp packages, especially via
node-gyp.

Solution: add gyp definition

This works only for Windows, OS/X, and Linux. We set a single
macro in project.gyp according to the system, and the rest is
done in builds/gyp/platform.hpp. The values in that file are
not dynamic. Your mileage will vary.

Solution: update to 2016

Of course people still "can" distributed the sources under the
LGPLv3. However we provide COPYING.LESSER with additional grants.

Solution: specify these grants in the header of each source file.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Macro ZMQ_VERSION represents the current version of 0MQ
Macro ZMQ_MAKE_VERSION(major,minor,patch) allows to create
a representation of the specified version.
The versions can be compared using simple <, >, ==, etc.
operators.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>