Support extended clipboard transfers

Implements support in both client and server for the extended
clipboard format first seen in UltraVNC. Currently only implements
text handling, but that is still an improvement as it extends the
clipboard from ISO 8859-1 to full Unicode.
diff --git a/common/rfb/SMsgReader.h b/common/rfb/SMsgReader.h
index 146b29f..4991fd3 100644
--- a/common/rfb/SMsgReader.h
+++ b/common/rfb/SMsgReader.h
@@ -1,5 +1,5 @@
 /* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
- * Copyright 2009-2014 Pierre Ossman for Cendio AB
+ * Copyright 2009-2019 Pierre Ossman for Cendio AB
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -54,6 +54,7 @@
     void readKeyEvent();
     void readPointerEvent();
     void readClientCutText();
+    void readExtendedClipboard(rdr::S32 len);
 
     void readQEMUMessage();
     void readQEMUKeyEvent();