Rate recorder trace helper

Also a small change in CCNx trace API
diff --git a/model/ccnx.h b/model/ccnx.h
index f87da94..8d565c1 100644
--- a/model/ccnx.h
+++ b/model/ccnx.h
@@ -197,14 +197,14 @@
   ////////////////////////////////////////////////////////////////////
   ////////////////////////////////////////////////////////////////////
 
-  TracedCallback<Ptr<const CcnxContentObjectHeader>,
+  TracedCallback<Ptr<const CcnxContentObjectHeader>, Ptr<const Packet>,
                  bool /*from cache*/,
                  Ptr<const CcnxFace> > m_outData;
 
-  TracedCallback<Ptr<const CcnxContentObjectHeader>,
+  TracedCallback<Ptr<const CcnxContentObjectHeader>, Ptr<const Packet>,
                  Ptr<const CcnxFace> > m_inData;
 
-  TracedCallback<Ptr<const CcnxContentObjectHeader>,
+  TracedCallback<Ptr<const CcnxContentObjectHeader>, Ptr<const Packet>,
                   DropReason,
                   Ptr<const CcnxFace> > m_dropData;  
 };