newbie question: unordered map missing?

Hello,

I'm poking around in the library for something like a hashmap and I
found this file:

http://www.boost.org/doc/libs/1_35_0/boost/interprocess/indexes/unordered_map_index.hpp

(boost/interprocess/indexes/unordered_map_index.hpp)

which includes this:  #include <boost/unordered_map.hpp>

which doesn't exist.

Where can I find this file?

Thank you
-Julie