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/CMsgHandler.h b/common/rfb/CMsgHandler.h
index effdaab..1581f79 100644
--- a/common/rfb/CMsgHandler.h
+++ b/common/rfb/CMsgHandler.h
@@ -70,7 +70,7 @@
     virtual void setColourMapEntries(int firstColour, int nColours,
 				     rdr::U16* rgbs) = 0;
     virtual void bell() = 0;
-    virtual void serverCutText(const char* str, rdr::U32 len) = 0;
+    virtual void serverCutText(const char* str) = 0;
 
     virtual void setLEDState(unsigned int state);