Solution: update (with correct one from VS2015)

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.)

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.)

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

- zmq_utils.h was removed
- udp_address.cpp and udp_engine.cpp were added

Solution: patch all affected build scripts

Solution: add these new classes to MSVC project files

Solution: fix and try again.

(We could start to think of using zproject to generate these build
scripts as the only difference is C/C++)

Solution: fix it.

Solution: add Iphlpapi.lib to libraries to link against

Solution: add these

Solution: add to project dependencies

also fixes issue https://github.com/zeromq/libzmq/issues/1624

Solution: increased to 4096 by default for all MSVC builds, for MinGW,
and for CMake.

Note: this is a speculative change, it needs confirmation before we
can keep it. Particularly, there is some doubt that changing this in
libzmq will affect upstream applications using libzmq.dll.

This became necessary after b9c27481

This became necessary after 22d6a974