signature-info: Fix encoding of type-specific TLV

This commit also introduces operator<< for SignatureInfo

Change-Id: Iddf5b77d9dab9f7b1764500726e6d5b1e13aedbb
Refs: #3914
diff --git a/src/signature-info.hpp b/src/signature-info.hpp
index 4ee8e64..fc99542 100644
--- a/src/signature-info.hpp
+++ b/src/signature-info.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2013-2015 Regents of the University of California.
+ * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -145,8 +145,14 @@
   std::list<Block> m_otherTlvs;
 
   mutable Block m_wire;
+
+  friend std::ostream&
+  operator<<(std::ostream& os, const SignatureInfo& info);
 };
 
+std::ostream&
+operator<<(std::ostream& os, const SignatureInfo& info);
+
 } // namespace ndn
 
 #endif // NDN_SIGNATURE_INFO_HPP