Some of our FreeBSD systems (like 10.0 and 10.1) have:

/usr/include/edit/readline/readline.h
 (NetBSD licensed version)

/usr/include/readline/readline.h
  (GNU-licensed)

The libraries are:
/usr/lib/libedit.so
/usr/lib/libreadline.so

Older FreeBSD 6.3 has the libreadline.so  but also has the libedit
at /lib/libedit.so.5.

Sorry I don't know if we use any readline feature that is not in the 
that older libedit. The old header is /usr/include/histedit.h.