table: fix Pit::erase crash when Interest name contains implicit digest

refs #3608

Change-Id: I41e0cd327b9dcc5f2d3a83f4cebff40c2d302fc1
diff --git a/daemon/table/pit-entry.hpp b/daemon/table/pit-entry.hpp
index ece0b40..e432c4e 100644
--- a/daemon/table/pit-entry.hpp
+++ b/daemon/table/pit-entry.hpp
@@ -38,6 +38,8 @@
 class Entry;
 } // namespace name_tree
 
+class Pit;
+
 namespace pit {
 
 /** \brief an unordered collection of in-records
@@ -198,6 +200,7 @@
 
   friend class nfd::NameTree;
   friend class nfd::name_tree::Entry;
+  friend class nfd::Pit;
 };
 
 inline const Interest&