all: Adding typedefs near forward declarations of Interest/ContentObject/Name

refs #29
diff --git a/utils/tracers/ndn-cs-tracer.h b/utils/tracers/ndn-cs-tracer.h
index ff5fc89..eb6f0b3 100644
--- a/utils/tracers/ndn-cs-tracer.h
+++ b/utils/tracers/ndn-cs-tracer.h
@@ -42,6 +42,9 @@
 class Interest;
 class ContentObject;
 
+typedef Interest InterestHeader;
+typedef ContentObject ContentObjectHeader;
+
 namespace cs {
 
 struct Stats