Add WinXP compatibility

#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)"

src/condition_variable.hpp

@@ -81,9 +81,15 @@ namespace zmq
 
 #else
 
+#ifdef ZMQ_HAVE_WINDOWS_TARGET_XP
+#include <condition_variable> 
+#include <mutex> 
+#endif
+
 namespace zmq
 {
 
+#ifndef ZMQ_HAVE_WINDOWS_TARGET_XP
     class condition_variable_t
     {
     public:
@@ -126,7 +132,54 @@ namespace zmq
         condition_variable_t (const condition_variable_t&);
         void operator = (const condition_variable_t&);
     };
+#else
+	class condition_variable_t
+	{
+	public:
+		inline condition_variable_t()
+		{
+
+		}
+
+		inline ~condition_variable_t()
+		{
+
+		}
+
+		inline int wait(mutex_t* mutex_, int timeout_)
+		{
+			std::unique_lock<std::mutex> lck(mtx);  // lock mtx
+			mutex_->unlock();                       // unlock mutex_ 
+			int res = 0;
+			if(timeout_ == -1) {
+				cv.wait(lck);                       // unlock mtx and wait cv.notify_all(), lock mtx after cv.notify_all()
+			} else if (cv.wait_for(lck, std::chrono::milliseconds(timeout_)) == std::cv_status::timeout) {
+				// time expired
+				errno = EAGAIN;
+				res = -1;
+			}
+			lck.unlock();                           // unlock mtx
+			mutex_->lock();                         // lock mutex_
+			return res;
+		}
+
+		inline void broadcast()
+		{
+			std::unique_lock<std::mutex> lck(mtx);  // lock mtx
+			cv.notify_all();
+		}
+
+	private:
+
+		std::condition_variable cv;
+		std::mutex mtx;
+
+		//  Disable copy construction and assignment.
+		condition_variable_t(const condition_variable_t&);
+		void operator = (const condition_variable_t&);
+	};
 
+#endif
 }
 
 #endif

src/tcp_address.cpp

@@ -245,7 +245,9 @@ int zmq::tcp_address_t::get_interface_name(unsigned long index, char ** dest) co
 	
 	char * if_name_result = NULL;
 
+#ifndef ZMQ_HAVE_WINDOWS_TARGET_XP
 	if_name_result = if_indextoname(index, buffer);
+#endif
 	
 	if (if_name_result == NULL) {
 		free(buffer);