That code is from David Ponce:

2003-04-27  David Ponce  <david@dponce.com>

        * recentf.el

        Major rewrite.  The code is reordered, cleaner and faster.
        Introduce new options to automatically cleanup the recent list,
        and to handle filename transformation (for example to use true
        filenames).

I imagine I did commit it in the old CVS.