all: InterestHeader and ContentObjectHeader refactoring to Interest and ContentObject

refs #29
diff --git a/examples/custom-apps/hijacker.cc b/examples/custom-apps/hijacker.cc
index 252cf92..4213f97 100644
--- a/examples/custom-apps/hijacker.cc
+++ b/examples/custom-apps/hijacker.cc
@@ -45,7 +45,7 @@
 }
 
 void
-Hijacker::OnInterest (const Ptr<const ndn::InterestHeader> &interest, Ptr<Packet> packet)
+Hijacker::OnInterest (const Ptr<const ndn::Interest> &interest, Ptr<Packet> packet)
 {
   ndn::App::OnInterest (interest, packet); // forward call to perform app-level tracing
   // do nothing else (hijack interest)