table: declare name_tree::Range type

Declare that NameTree enumeration returns name_tree::Range type
instead of an unspecified type usable with range-based for.

refs #3738

Change-Id: I132c583704d0c6164077abf70a694e833b448e85
diff --git a/daemon/table/name-tree-iterator.hpp b/daemon/table/name-tree-iterator.hpp
index ecde5bd..cb0921d 100644
--- a/daemon/table/name-tree-iterator.hpp
+++ b/daemon/table/name-tree-iterator.hpp
@@ -195,6 +195,13 @@
   EntrySelector m_pred;
 };
 
+/** \brief a Forward Range of name tree entries
+ *
+ *  This type has .begin() and .end() methods which return Iterator.
+ *  This type is usable with range-based for.
+ */
+typedef boost::iterator_range<Iterator> Range;
+
 } // namespace name_tree
 } // namespace nfd