table: NameTree::getEntry

NameTree::get is renamed to NameTree::lookup.
NameTree::getEntry is introduced to return the NameTreeEntry on which a table entry is attached.
tableEntry::m_nameTreeEntry is changed to weak_ptr to avoid circular shared_ptr reference.

refs #3608, #3619

Change-Id: I425b6a2eb5fe3024bbaff4ff766eb6739be54b02
diff --git a/daemon/table/measurements-entry.hpp b/daemon/table/measurements-entry.hpp
index f2dd627..0c9bc48 100644
--- a/daemon/table/measurements-entry.hpp
+++ b/daemon/table/measurements-entry.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2014-2015,  Regents of the University of California,
+ * Copyright (c) 2014-2016,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -36,7 +36,7 @@
 
 namespace name_tree {
 class Entry;
-}
+} // namespace name_tree
 
 class Measurements;
 
@@ -60,7 +60,7 @@
 private: // lifetime
   time::steady_clock::TimePoint m_expiry;
   scheduler::EventId m_cleanup;
-  shared_ptr<name_tree::Entry> m_nameTreeEntry;
+  weak_ptr<name_tree::Entry> m_nameTreeEntry;
 
   friend class nfd::NameTree;
   friend class nfd::name_tree::Entry;