Add vs2013 solution and build for (v120) of libzmq project.
fix test_fork

* was problem on debian/wheezy
Merge pull request #933 from soundart/master

cmake: fix test_fork
Visual Studio 2013 build updates.
Merge pull request #934 from evoskuil/master

Add Visual Studio 2013 solution and build for (v120) of libzmq project.
cmake: fix fragile code related to HAVE_FORK macro

* report from Richard Newton indicated previous solutions was not
  working on Windows
Merge pull request #936 from soundart/master

cmake: fix test_fork,  fix fragile code related to HAVE_FORK macro