Display partial updates on slow transfers

Normally we only display screen changes once we have the updates for
the entire screen. This may give the impression that the viewer is
hung though. So display the partial data if the update is taking to
long to arrive.
diff --git a/vncviewer/CConn.h b/vncviewer/CConn.h
index 1b92937..06e3040 100644
--- a/vncviewer/CConn.h
+++ b/vncviewer/CConn.h
@@ -81,6 +81,8 @@
 
   static void handleOptions(void *data);
 
+  static void handleUpdateTimeout(void *data);
+
 private:
   char* serverHost;
   int serverPort;