tracers: Extending helper API in tracers

Now all tracers can be installed on individual nodes.

It is also possible to specify "-" as a file name, leading to tracing on
standard output.

Refs #1007 (http://redmine.named-data.net)
diff --git a/utils/tracers/ndn-l3-rate-tracer.h b/utils/tracers/ndn-l3-rate-tracer.h
index 4db4e70..64e5177 100644
--- a/utils/tracers/ndn-l3-rate-tracer.h
+++ b/utils/tracers/ndn-l3-rate-tracer.h
@@ -25,6 +25,7 @@
 
 #include "ns3/nstime.h"
 #include "ns3/event-id.h"
+#include <ns3/node-container.h>
 
 #include <boost/tuple/tuple.hpp>
 #include <boost/shared_ptr.hpp>
@@ -63,7 +64,7 @@
   /**
    * @brief Helper method to install tracers on all simulation nodes
    *
-   * @param file File to which traces will be written
+   * @param file File to which traces will be written.  If filename is -, then std::out is used
    * @param averagingPeriod Defines averaging period for the rate calculation,
    *        as well as how often data will be written into the trace file (default, every half second)
    *
@@ -74,6 +75,47 @@
   static boost::tuple< boost::shared_ptr<std::ostream>, std::list<Ptr<L3RateTracer> > >
   InstallAll (const std::string &file, Time averagingPeriod = Seconds (0.5));
 
+  /**
+   * @brief Helper method to install tracers on the selected simulation nodes
+   *
+   * @param nodes Nodes on which to install tracer
+   * @param file File to which traces will be written.  If filename is -, then std::out is used
+   * @param averagingPeriod How often data will be written into the trace file (default, every half second)
+   *
+   * @returns a tuple of reference to output stream and list of tracers. !!! Attention !!! This tuple needs to be preserved
+   *          for the lifetime of simulation, otherwise SEGFAULTs are inevitable
+   *
+   */
+  static boost::tuple< boost::shared_ptr<std::ostream>, std::list<Ptr<L3RateTracer> > >
+  Install (const NodeContainer &nodes, const std::string &file, Time averagingPeriod = Seconds (0.5));
+
+  /**
+   * @brief Helper method to install tracers on a specific simulation node
+   *
+   * @param nodes Nodes on which to install tracer
+   * @param file File to which traces will be written.  If filename is -, then std::out is used
+   * @param averagingPeriod How often data will be written into the trace file (default, every half second)
+   *
+   * @returns a tuple of reference to output stream and list of tracers. !!! Attention !!! This tuple needs to be preserved
+   *          for the lifetime of simulation, otherwise SEGFAULTs are inevitable
+   *
+   */
+  static boost::tuple< boost::shared_ptr<std::ostream>, std::list<Ptr<L3RateTracer> > >
+  Install (Ptr<Node> node, const std::string &file, Time averagingPeriod = Seconds (0.5));
+
+  /**
+   * @brief Helper method to install tracers on a specific simulation node
+   *
+   * @param nodes Nodes on which to install tracer
+   * @param outputStream Smart pointer to a stream
+   * @param averagingPeriod How often data will be written into the trace file (default, every half second)
+   *
+   * @returns a tuple of reference to output stream and list of tracers. !!! Attention !!! This tuple needs to be preserved
+   *          for the lifetime of simulation, otherwise SEGFAULTs are inevitable
+   */
+  static Ptr<L3RateTracer>
+  Install (Ptr<Node> node, boost::shared_ptr<std::ostream> outputStream, Time averagingPeriod = Seconds (0.5));
+  
   // from L3Tracer
   virtual void
   PrintHeader (std::ostream &os) const;
@@ -84,40 +126,31 @@
 protected:
   // from L3Tracer
   virtual void
-  OutInterests  (std::string context,
-                 Ptr<const Interest>, Ptr<const Face>);
+  OutInterests  (Ptr<const Interest>, Ptr<const Face>);
 
   virtual void
-  InInterests   (std::string context,
-                 Ptr<const Interest>, Ptr<const Face>);
+  InInterests   (Ptr<const Interest>, Ptr<const Face>);
 
   virtual void
-  DropInterests (std::string context,
-                 Ptr<const Interest>, Ptr<const Face>);
+  DropInterests (Ptr<const Interest>, Ptr<const Face>);
 
   virtual void
-  OutNacks  (std::string context,
-             Ptr<const Interest>, Ptr<const Face>);
+  OutNacks  (Ptr<const Interest>, Ptr<const Face>);
 
   virtual void
-  InNacks   (std::string context,
-             Ptr<const Interest>, Ptr<const Face>);
+  InNacks   (Ptr<const Interest>, Ptr<const Face>);
 
   virtual void
-  DropNacks (std::string context,
-             Ptr<const Interest>, Ptr<const Face>);
+  DropNacks (Ptr<const Interest>, Ptr<const Face>);
 
   virtual void
-  OutData  (std::string context,
-            Ptr<const ContentObject>, Ptr<const Packet>, bool fromCache, Ptr<const Face>);
+  OutData  (Ptr<const ContentObject>, Ptr<const Packet>, bool fromCache, Ptr<const Face>);
 
   virtual void
-  InData   (std::string context,
-            Ptr<const ContentObject>, Ptr<const Packet>, Ptr<const Face>);
+  InData   (Ptr<const ContentObject>, Ptr<const Packet>, Ptr<const Face>);
 
   virtual void
-  DropData (std::string context,
-            Ptr<const ContentObject>, Ptr<const Packet>, Ptr<const Face>);
+  DropData (Ptr<const ContentObject>, Ptr<const Packet>, Ptr<const Face>);
 
   virtual void
   SatisfiedInterests (Ptr<const pit::Entry>);