Clean up internal clipboard handling

We now filter incoming data, which means we can start assuming the
clipboard data is always null terminated. This allows us to clean
up a lot of the internal handling.
diff --git a/common/rfb/CMsgWriter.h b/common/rfb/CMsgWriter.h
index 4d533d4..d3ac19c 100644
--- a/common/rfb/CMsgWriter.h
+++ b/common/rfb/CMsgWriter.h
@@ -55,7 +55,7 @@
 
     void writeKeyEvent(rdr::U32 keysym, rdr::U32 keycode, bool down);
     void writePointerEvent(const Point& pos, int buttonMask);
-    void writeClientCutText(const char* str, rdr::U32 len);
+    void writeClientCutText(const char* str);
 
   protected:
     void startMsg(int type);