Automatic lossless refresh

Resend pixel perfect copies of areas that were previously sent
using a lossy encoder. This is done when there is no normal update
to send, and no congestion.
diff --git a/common/rfb/Encoder.h b/common/rfb/Encoder.h
index a8a447e..66a10d2 100644
--- a/common/rfb/Encoder.h
+++ b/common/rfb/Encoder.h
@@ -35,6 +35,8 @@
     // Give us the raw frame buffer, and not something converted to
     // the what the client is asking for.
     EncoderUseNativePF = 1 << 0,
+    // Encoder does not encode pixels perfectly accurate
+    EncoderLossy = 1 << 1,
   };
 
   class Encoder {