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/RREEncoder.h b/common/rfb/RREEncoder.h
index b263967..487344f 100644
--- a/common/rfb/RREEncoder.h
+++ b/common/rfb/RREEncoder.h
@@ -25,7 +25,7 @@
 
   class RREEncoder : public RawEncoder {
   public:
-    RREEncoder(SMsgWriter* writer);
+    RREEncoder(SConnection* conn);
     virtual ~RREEncoder();
     virtual void writeRect(const Rect& r, TransImageGetter* ig);
   private: