Inherit SocketServer directly from VNCServer

This makes VNCServer a sufficiently complete interface that callers
don't need to know about the specific implementation (VNCServerST
currently). And assuming that all servers will use sockets is not
that outrageous.
diff --git a/unix/x0vncserver/XDesktop.h b/unix/x0vncserver/XDesktop.h
index dc616e9..7d06061 100644
--- a/unix/x0vncserver/XDesktop.h
+++ b/unix/x0vncserver/XDesktop.h
@@ -21,7 +21,7 @@
 #ifndef __XDESKTOP_H__
 #define __XDESKTOP_H__
 
-#include <rfb/VNCServerST.h>
+#include <rfb/SDesktop.h>
 #include <tx/TXWindow.h>
 #include <unixcommon.h>
 
@@ -70,7 +70,7 @@
   Display* dpy;
   Geometry* geometry;
   XPixelBuffer* pb;
-  rfb::VNCServerST* server;
+  rfb::VNCServer* server;
   QueryConnectDialog* queryConnectDialog;
   network::Socket* queryConnectSock;
   int oldButtonMask;