Introduce Denial-of-Existence (DoE) for Nack response.

Note this commit changes how names are stored in the database, compliant
to the canonical order.

Change-Id: I9857aaefc1f7da08ff53eff43c8f8c8bd5443953
Refs: #4152
diff --git a/src/ndns-enum.cpp b/src/ndns-enum.cpp
index 383eb95..37a5b7d 100644
--- a/src/ndns-enum.cpp
+++ b/src/ndns-enum.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2014-2016, Regents of the University of California.
+/*
+ * Copyright (c) 2014-2018, Regents of the University of California.
  *
  * This file is part of NDNS (Named Data Networking Domain Name Service).
  * See AUTHORS.md for complete list of NDNS authors and contributors.
@@ -35,6 +35,9 @@
   case NDNS_NACK:
     os << "NACK";
     break;
+  case NDNS_DOE:
+    os << "DOE";
+    break;
   case NDNS_KEY:
     os << "KEY";
     break;