all: InterestHeader and ContentObjectHeader refactoring to Interest and ContentObject

refs #29
diff --git a/apps/ndn-producer.h b/apps/ndn-producer.h
index f383643..bce01d3 100644
--- a/apps/ndn-producer.h
+++ b/apps/ndn-producer.h
@@ -48,7 +48,7 @@
   Producer ();
 
   // inherited from NdnApp
-  void OnInterest (const Ptr<const InterestHeader> &interest, Ptr<Packet> packet);
+  void OnInterest (const Ptr<const Interest> &interest, Ptr<Packet> packet);
 
 protected:
   // inherited from Application base class.