util: InMemoryStorage::insert requires Data wire encoding

refs #2639

Change-Id: Ie151c8e05623ea73d3b2f2cd9343a4c3f0bacb53
diff --git a/src/util/in-memory-storage.hpp b/src/util/in-memory-storage.hpp
index bdc3962..0b6e523 100644
--- a/src/util/in-memory-storage.hpp
+++ b/src/util/in-memory-storage.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2013-2016 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).
  *
@@ -104,7 +104,8 @@
   class Error : public std::runtime_error
   {
   public:
-    Error() : std::runtime_error("Cannot reduce the capacity of the in-memory storage!")
+    Error()
+      : std::runtime_error("Cannot reduce the capacity of the in-memory storage!")
     {
     }
   };
@@ -130,7 +131,7 @@
 
   /** @brief Inserts a Data packet
    *
-   *  @param data the packet to insert
+   *  @param data the packet to insert, must be signed and have wire encoding
    *  @param mustBeFreshProcessingWindow Beyond this time period after the data is inserted, the
    *         data can only be used to answer interest without MustBeFresh selector.
    *