Solution: Rename the custom implementation of clock_gettime for macOS to
alt_clock_gettime and wrap all usage in preprocessor macros to only enable the
alternative version when using macOS <= 10.11.

This issue occurs when targeting macOS 10.11 or earlier but using the 10.12
or newer SDK.

Problem: build API incompatible with 4.1

Solution: keep the new --without-docs option, but also keep the old
--without-documentation with an added deprecation warning.
We can then remove it in the next major release, to leave enough time
for users and maintainers to change it without disruptions.

Problem: 2 connects with same sourceip:port to different destip:port fail

Solution: during a connect with a TCP endpoint if a source address is
passed set the SO_REUSEADDR flag on the socket before the bind system
call.
Add unit test to cover this case for both IPv4 and IPv6.

Update INSTALL to note issues with 'make -j check'

Some of the tests cannot be run in parallel; until the Makefile is fixed, note this in INSTALL.

Problem: Does not build in Visual Studio 2013 / Win32

Solution: #include <netioapi.h> and change some IP_ADAPTER_UNICAST_ADDRESS data types

Add EHOSTUNREACH to errno_to_string

performance enhancement

use clock_gettime if there is no instruction to get cpu tick. It will take about 10% performance enhancement in AIX 7.1.

* - Fixed windows build errors
- Extended monitor lock scope to prevent race-condition between
  process_stop and monitor

* - Fixed windows build errors
- Extended monitor lock scope to prevent race-condition between
  process_stop and monitor

#2158: Add mutex for monitor socket

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