utils: Enable use of the simulation time in NFD

Conversion of ndnSIM time to system_clock::time_point, steady_clock::time_point, so that NFD use the simulation time.
diff --git a/utils/ndn-time.cpp b/utils/ndn-time.cpp
new file mode 100644
index 0000000..075b1a9
--- /dev/null
+++ b/utils/ndn-time.cpp
@@ -0,0 +1,71 @@
+/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2012-2014 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include "ndn-time.hpp"
+
+#include "ns3/simulator.h"
+
+namespace ns3 {
+namespace ndn {
+namespace time {
+
+system_clock::time_point
+CustomSystemClock::getNow() const
+{
+  boost::chrono::nanoseconds ns(Simulator::Now().GetNanoSeconds());
+  return system_clock::time_point(ns);
+}
+
+std::string
+CustomSystemClock::getSince() const
+{
+  return " since start of simulation";
+}
+
+boost::posix_time::time_duration
+CustomSystemClock::toPosixDuration(const system_clock::duration& duration) const
+{
+  BOOST_ASSERT_MSG(false, "Must not be called");
+  return boost::posix_time::microseconds(1);
+}
+
+////////////////////////////////////
+
+steady_clock::time_point
+CustomSteadyClock::getNow() const
+{
+  boost::chrono::nanoseconds ns(Simulator::Now().GetNanoSeconds());
+  return steady_clock::time_point(ns);
+}
+
+std::string
+CustomSteadyClock::getSince() const
+{
+  return " since start of simulation";
+}
+
+boost::posix_time::time_duration
+CustomSteadyClock::toPosixDuration(const steady_clock::duration& duration) const
+{
+  BOOST_ASSERT_MSG(false, "Must not be called");
+  return boost::posix_time::microseconds(1);
+}
+
+} // namespace time
+} // namespace ndn
+} // namespace ns3