Encoders/decoders should track the connection object

The connection object is a much more appropriate object for the
decoders and encoders to keep track of. Besides the streams, it also
contains state like connection parameters.
diff --git a/common/rfb/ZRLEDecoder.h b/common/rfb/ZRLEDecoder.h
index dee2068..e7e2b8c 100644
--- a/common/rfb/ZRLEDecoder.h
+++ b/common/rfb/ZRLEDecoder.h
@@ -25,7 +25,7 @@
 
   class ZRLEDecoder : public Decoder {
   public:
-    ZRLEDecoder(CMsgReader* reader);
+    ZRLEDecoder(CConnection* conn);
     virtual ~ZRLEDecoder();
     virtual void readRect(const Rect& r, CMsgHandler* handler);
   private: