Export the functions SupportsClient2Server and SupportsServer2Client

These are useful functions for VNC clients, so let's export them for
everybody to use.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

rfb/rfbclient.h

@@ -285,6 +285,9 @@ extern rfbBool PermitServerInput(rfbClient* client, int enabled);
 
 extern void PrintPixelFormat(rfbPixelFormat *format);
 
+extern rfbBool SupportsClient2Server(rfbClient* client, int messageType);
+extern rfbBool SupportsServer2Client(rfbClient* client, int messageType);
+
 /* client data */
 
 void rfbClientSetClientData(rfbClient* client, void* tag, void* data);