Always use IPv6 for the server if a "dual stack" is available. This means a server on vista (as well as most linux systems) will support IPv6 by default. IPv4 requests will be mapped by the OS.

src/net/socket_helper.h

@@ -35,6 +35,10 @@
 #define SOCKET_ERR_NOTCONN		WSAENOTCONN
 #define SOCKET_ERR_NOTSOCK		WSAENOTSOCK
 
+#ifndef IPV6_V6ONLY
+	#define IPV6_V6ONLY			27
+#endif
+
 #ifdef __GNUC__ /* mingw provides stdint.h */
 	#include <stdint.h>
 	typedef uint16_t			u_int16_t;