#define ZMQ_HAVE_WINDOWS_TARGET_XP  disable uncompatible WinAPI

1. Disable call if_indextoname()
2. Emulate windows Condition Variable API in class condition_variable_t with std::condition_variable
 	
This code can be compiled in MSVC 2015 with option "Platform toolset: Visual Studio 2015 - Windows XP (v140_xp)"