Bug#731637: compatibility patch with 4.01beta for Frama-C Fluorine

[Pascal Cuoq]

Note that a patch to Frama-C Fluorine3 20130601 to make it compile with
OCaml 4.01 is available from
https://github.com/vprevosto/opam-repository/blob/master/packages/frama-c.20130601/files/4.01-compat.patch