Issue #25   Replacing usage of TCP RTT estimator with a customized version

In the current commit, RTT estimator does not implement Karn's algorithm
and takes into account all RTT samples, including ambiguous samples from
retransmitted Interests.
diff --git a/apps/ndn-consumer.cc b/apps/ndn-consumer.cc
index 3a14e48..1b85cfb 100644
--- a/apps/ndn-consumer.cc
+++ b/apps/ndn-consumer.cc
@@ -33,6 +33,7 @@
 #include "ns3/ndn-interest.h"
 #include "ns3/ndn-content-object.h"
 #include "ns3/ndnSIM/utils/ndn-fw-hop-count-tag.h"
+#include "ns3/ndnSIM/utils/ndn-rtt-mean-deviation.h"
 
 #include <boost/ref.hpp>
 #include <boost/lexical_cast.hpp>