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/TightEncoder.h b/common/rfb/TightEncoder.h
index b633512..8a58985 100644
--- a/common/rfb/TightEncoder.h
+++ b/common/rfb/TightEncoder.h
@@ -58,7 +58,7 @@
   
   class TightEncoder : public Encoder {
   public:
-    TightEncoder(SMsgWriter* writer);
+    TightEncoder(SConnection* conn);
     virtual ~TightEncoder();
 
     virtual void setCompressLevel(int level);