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/VNCServer.h b/common/rfb/VNCServer.h
index 298326f..5398e9f 100644
--- a/common/rfb/VNCServer.h
+++ b/common/rfb/VNCServer.h
@@ -57,7 +57,7 @@
 
     // serverCutText() tells the server that the cut text has changed.  This
     // will normally be sent to all clients.
-    virtual void serverCutText(const char* str, int len) = 0;
+    virtual void serverCutText(const char* str) = 0;
 
     // bell() tells the server that it should make all clients make a bell sound.
     virtual void bell() = 0;