Small update of PIT. Now pit implementation is policy-templated.

Three versions are explicitly instantiated:
- CcnxPitImpl<persistent_policy_traits> ("ns3::CcnxPit")
- CcnxPitImpl<random_policy_traits>     ("ns3::CcnxPitRandom")
- CcnxPitImpl<lru_policy_traits>        ("ns3::CcnxPitLru")
diff --git a/model/pit/ccnx-pit-impl.h b/model/pit/ccnx-pit-impl.h
index 2f52604..94709f3 100644
--- a/model/pit/ccnx-pit-impl.h
+++ b/model/pit/ccnx-pit-impl.h
@@ -24,8 +24,6 @@
 #include "ccnx-pit.h"
 
 #include "../../utils/trie-with-policy.h"
-#include "../../utils/empty-policy.h"
-#include "../../utils/persistent-policy.h"
 
 #include "ccnx-pit-entry-impl.h"
 
@@ -37,18 +35,21 @@
  * \ingroup ccnx
  * \brief Class implementing Pending Interests Table
  */
+template<class Policy>
 class CcnxPitImpl : public CcnxPit
                   , protected ndnSIM::trie_with_policy<CcnxNameComponents,
-                                                       ndnSIM::smart_pointer_payload_traits<CcnxPitEntryImpl< CcnxPitImpl > >,
-                                                       ndnSIM::persistent_policy_traits
+                                                       ndnSIM::smart_pointer_payload_traits<CcnxPitEntryImpl< CcnxPitImpl< Policy > > >,
+                                                       // ndnSIM::persistent_policy_traits
+                                                       Policy
                                                        >
 {
 public:
   typedef ndnSIM::trie_with_policy<CcnxNameComponents,
-                                   ndnSIM::smart_pointer_payload_traits<CcnxPitEntryImpl< CcnxPitImpl > >,
-                                   ndnSIM::persistent_policy_traits
+                                   ndnSIM::smart_pointer_payload_traits<CcnxPitEntryImpl< CcnxPitImpl< Policy > > >,
+                                   // ndnSIM::persistent_policy_traits
+                                   Policy
                                    > super;
-  typedef CcnxPitEntryImpl< CcnxPitImpl > entry;
+  typedef CcnxPitEntryImpl< CcnxPitImpl< Policy > > entry;
 
   /**
    * \brief Interface ID