Use correct winsock header

We link to ws2_32.lib which corresponds to the winsock2.h header, not the
winsock.h header.

[JES: fixed commit message]
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

rfb/rfbproto.h

@@ -65,7 +65,7 @@
 #define LIBVNCSERVER_WORDS_BIGENDIAN
 #define rfbBool int
 #include <sys/timeb.h>
-#include <winsock.h>
+#include <winsock2.h>
 #undef SOCKET
 #define SOCKET int
 #else