Fixed issue #2155

Added fallback mechanism for specific socket binding on Windows platform with IPv6 enabled

# Conflicts:
#	builds/msvc/vs2012/libsodium.import.props

Patch for compatibility with Windows subsystem for linux

Problem: Invalid markup in zmq_socket.txt

Solution: Fix it.

Problem: a request

Solution: honor it

doc/zmq_socket.txt: clarify that ROUTER can be blocking

Fix zmq poller poll return

* Doing so was zmq_poller_poll to always return 0.

allow duplicate entries in zmq_poller_poll

This should restore full compatibility with earlier zmq_poll behavior.

It complicates things a little bit, as collisions must be detected, and when collisions are found:

- event masks must be merged
- pollitems, events arrays are no longer co-ordered

Reverts the recent zmq_proxy patch to workaround the lack of repeat-item support in zmq_poll that is now fixed.

Resolve issues with zmq_poll and zmq_poller working together

not -1, ETIMEDOUT like zmq_poller

Return value is the number of events found. This also propagates to the return value of zmq_poller_wait_all.

zmq_poller_wait was only returning events on the first-registered socket.

avoid passing duplicate entries to zmq_poll

zmq_poller doesn't allow a socket to appear twice

heap-allocate events in zmq_poller_poll

variable-size array allocation is not allowed by some compilers

Support all sockets in zmq_poll

only define clock macros on darwin if not already defined

update socket_poller when ZMQ_POLL_BASED_ON_SELECT

enables zmq_poll on threadsafe sockets only supported in zmq_poller (radio, dish, etc.)

previous patch updated only the branch for ZMQ_POLL_BASED_ON_POLL, causing failed builds on Windows.

clang from Xcode 8 has these already defined, causing duplicate macro warnings

Problem: Brocade has copyright but not in AUTHORS and RELICENSE

Problem: pkg-config Requires.private is broken

Solution: add it. Some of the work that I do happens during working
hours and hence the copyright belongs to my employer, Brocade
Communications Systems Inc. Note this in the AUTHORS file.

Solution: use only Libs.private to avoid breaking application builds.
Even though Requires.private are supposed to be parsed only if
pkg-config is called with --static, the --cflags parameter is enough
to trigger the parsing, causing build failures for applications that
do not (and should not) depend on libzmq's dependencies.

Problem: pkgconfig file does not support static link

Solution: add dependencies, if necessary, to the .private Libs and
Requires field of the pkgconfig file at build time.
This way pkg-config --static --libs libzmq will correctly print
dependencies if they were used to build the static libzmq.a library.

pass through poller events