tracers+docs: Correcting compilation and installation of trace helpers

Also in this commit an example on how to use trace helpers, including
how to build graphs using R.
diff --git a/examples/ndn-tree-tracers.cc b/examples/ndn-tree-tracers.cc
new file mode 100644
index 0000000..b76869a
--- /dev/null
+++ b/examples/ndn-tree-tracers.cc
@@ -0,0 +1,125 @@
+/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2011-2012 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ */
+
+// ndn-tree-tracers.cc
+
+#include "ns3/core-module.h"
+#include "ns3/network-module.h"
+#include "ns3/ndnSIM-module.h"
+
+// for ndn::L3AggregateTracer
+#include <ns3/ndnSIM/utils/tracers/ndn-l3-aggregate-tracer.h>
+
+// for ndn::L3RateTracer
+#include <ns3/ndnSIM/utils/tracers/ndn-l3-rate-tracer.h>
+
+using namespace ns3;
+
+/**
+ * This scenario simulates a tree topology (using topology reader module)
+ *
+ *    /------\      /------\      /------\      /------\
+ *    |leaf-1|      |leaf-2|      |leaf-3|      |leaf-4|
+ *    \------/      \------/      \------/      \------/
+ *         ^          ^                ^           ^	
+ *         |          |                |           |
+ *    	    \        /                  \         / 
+ *           \      /  			 \  	 /    10Mbps / 1ms
+ *            \    /  			  \ 	/
+ *             |  |  			   |   | 
+ *    	       v  v                        v   v     
+ *          /-------\                    /-------\
+ *          | rtr-1 |                    | rtr-2 |
+ *          \-------/                    \-------/
+ *                ^                        ^                      
+ *      	  |	 		   |
+ *      	   \			  /  10 Mpbs / 1ms 
+ *      	    +--------+  +--------+ 
+ *      		     |  |      
+ *                           v  v
+ *      		  /--------\
+ *      		  |  root  |
+ *                        \--------/
+ *
+ *
+ * To run scenario and see what is happening, use the following command:
+ *
+ *     ./waf --run=ndn-tree-tracers
+ */
+
+int
+main (int argc, char *argv[])
+{
+  CommandLine cmd;
+  cmd.Parse (argc, argv);
+
+  AnnotatedTopologyReader topologyReader ("", 1);
+  topologyReader.SetFileName ("src/ndnSIM/examples/topologies/topo-tree.txt");
+  topologyReader.Read ();
+
+  // Install CCNx stack on all nodes
+  ndn::StackHelper ccnxHelper;
+  ccnxHelper.SetForwardingStrategy ("ns3::ndn::fw::BestRoute");
+  ccnxHelper.InstallAll ();
+
+  // Installing global routing interface on all nodes
+  ndn::GlobalRoutingHelper ccnxGlobalRoutingHelper;
+  ccnxGlobalRoutingHelper.InstallAll ();
+
+  // Getting containers for the consumer/producer
+  Ptr<Node> consumers[4] = { Names::Find<Node> ("leaf-1"), Names::Find<Node> ("leaf-2"),
+                             Names::Find<Node> ("leaf-3"), Names::Find<Node> ("leaf-4") };
+  Ptr<Node> producer = Names::Find<Node> ("root");
+
+  for (int i = 0; i < 4; i++)
+    {
+      ndn::AppHelper consumerHelper ("ns3::ndn::ConsumerCbr");
+      consumerHelper.SetAttribute ("Frequency", StringValue ("100")); // 100 interests a second
+
+      // Each consumer will express unique interests /root/<leaf-name>/<seq-no>
+      consumerHelper.SetPrefix ("/root/" + Names::FindName (consumers[i]));
+      consumerHelper.Install (consumers[i]);
+    }
+    
+  ndn::AppHelper producerHelper ("ns3::ndn::Producer");
+  producerHelper.SetAttribute ("PayloadSize", StringValue("1024"));  
+
+  // Register /root prefix with global routing controller and
+  // install producer that will satisfy Interests in /root namespace
+  ccnxGlobalRoutingHelper.AddOrigins ("/root", producer);
+  producerHelper.SetPrefix ("/root");
+  producerHelper.Install (producer);
+
+  // Calculate and install FIBs
+  ccnxGlobalRoutingHelper.CalculateRoutes ();
+
+  Simulator::Stop (Seconds (20.0));
+
+  boost::tuple< boost::shared_ptr<std::ostream>, std::list<Ptr<ndn::L3AggregateTracer> > >
+    aggTracers = ndn::L3AggregateTracer::InstallAll ("aggregate-trace.txt", Seconds (0.5));
+
+  boost::tuple< boost::shared_ptr<std::ostream>, std::list<Ptr<ndn::L3RateTracer> > >
+    rateTracers = ndn::L3RateTracer::InstallAll ("rate-trace.txt", Seconds (0.5));
+  
+  Simulator::Run ();
+  Simulator::Destroy ();
+
+  return 0;
+}