Revert some changes so that I can merge to master.

Revert "Rename iterator typedef to n_iterator." and "Combine some of the
headers."

This reverts commits: 2f6b81d8c1 and
e1b39bbbfb.

include/boost/unordered/unordered_map.hpp

@@ -17,6 +17,7 @@
 #include <boost/unordered/unordered_map_fwd.hpp>
 #include <boost/unordered/detail/equivalent.hpp>
 #include <boost/unordered/detail/unique.hpp>
+#include <boost/unordered/detail/util.hpp>
 #include <boost/functional/hash.hpp>
 #include <boost/move/move.hpp>