add tests and fix leak

src/core/ptr.cc

@@ -284,10 +284,12 @@ PtrTest::RunTests (void)
   {
     Ptr<NoCount> p = MakeNewObject<NoCount> (cb);
     Callback<void> callback = MakeCallback (&NoCount::Nothing, p);
+    callback ();
   }
   {
     Ptr<const NoCount> p = MakeNewObject<NoCount> (cb);
     Callback<void> callback = MakeCallback (&NoCount::Nothing, p);
+    callback ();
   }
 
 #if 0

src/core/ptr.h

@@ -179,11 +179,12 @@ struct CallbackTraits<Ptr<T> >
 {
   static T & GetReference (Ptr<T> const p)
   {
-    return *GetPointer (p);
+    return *PeekPointer (p);
   }
 };
 
 
+
 } // namespace ns3