mingw defaults with _WIN32_WINNT as 0x0502 which doesn't define inet_pton(), so add a conditional check

used static_cast<signed int> around WSA_WAIT_FAILED as it is an unsigned implicitly defined as (0xFFFFFFFF ion winbase.h) and causes a comparison error.

removed use of c++11 style initialiser list for 'sockaddr addr { 0 }' and changed it to 'sockaddr addr = { 0 }'

includes windows.hpp if on windows build for mingw build errors from including zmq.h before windows.h

Problem: CI builds libsodium from dev branch

Solution: checkout stable branch instead.
Several warnings are printed when building from the master branch,
and developers recommend using the stable branch instead.

Problem: commit a464eec7 really broke VS2015 builds

Took me over 8 hours to track down the cause of bizarre link
errors when building with libsodium. The VS project files are
not simple things.

Note to self and other maintainers: when someone is obviously
out of their depth, do not merge their changes to build scripts
without cynical appraisal.

Solution: undo the damage.

Problem: Valgrind reports read of freed memory

Solution: when iterating over a map and conditionally deleting
elements, an erased iterator gets invalidated. Call erase using postfix
increment on iterator to avoid using an invalid element in the next
iteration.

Problem: no support for pre-allocated file descriptors [systemd | upstart socket-based activation]

Solution: parse the value set by the ZMQ_PRE_ALLOCATED_FD sockopt
when creating a new TCP socket and use it if valid.
Add new tests/test_pre_allocated_fd_tcp.cpp unit test.

Solution: parse the value set by the ZMQ_PRE_ALLOCATED_FD sockopt
when creating a new IPC socket and use it if valid.
Add new tests/test_pre_allocated_fd_ipc.cpp unit test.

Solution: add new [set|get]sockopt ZMQ_PRE_ALLOCATED_FD to allow
users to let ZMQ use a pre-allocated file descriptor instead of
allocating a new one. Update [set|get]sockopt documentation and
test accordingly.

The main use case for this feature is a socket-activated systemd
service. For more information about this feature see:
http://0pointer.de/blog/projects/socket-activation.html

Problem: Android build is slow and noisy

Solution: use --without-docs (changed from --without-documentation)
and also --quiet.

Problem: MSVC build does not detect libsodium

Caused by error in last commit which used HAVE_LIBSODIUM instead
of HAVE_SODIUM.

Solution: use HAVE_LIBSODIUM as we do in other configure scripts.

The project is called 'libsodium' and not 'sodium'.

Windows command-line build is now configurable

There is an option to enable/disable libsodium via the Visual Studio
UI. This is not practical for command-line usage (via msbuild).

Solution: add configure.bat that searches for libsodium in sibling
directory to libzmq; if it finds it, defines HAVE_LIBSODIUM 1.

This is consistent with zproject, which has the same problem and
is getting the same solution for all dependency resolution on
Windows.

Note that this approach also provides a way to support tweetnacl
via a configure option.

Also, removed duplicate props files and re-copy in configure.bat
as it was an insane nightmare to update these by hand. (and not
clear that they were identical. Now it's forced.)

Solution: fix .gitignore

Solution: add myself to the list

Make VMCI work on Windows

configure doesn't correctly determine mingw64

select was improved to support multiple service providers on Windows.
it should be slightly faster because of optimized iteration
over selected sockets.

changes the search pattern for host_os from *mingw32* to *mingw* so that mingw64 can be used, and any mingw32 variable name change to mingw.

conformity update for mingw32 variables to mingw

changes the search pattern for host_os from *mingw32* to *mingw* so that mingw64 can be used

Fixed VS2015 build

Leading to extra work when copying between versions of VS.

Solution: remove second unnecessary definition.

Solution: add missing project files

(Also, updated FD_SETSIZE to 16K as a bonus.)

Problem: not building on VS2015

Solution: fixed project files, and warning in timers.cpp

Revert "Revert "Problem: deprecated use and reference of `zmq_term`""