Open MPI: version 1.8.2.

Upgrade Open MPI to version 1.8.2. For a summary of changes, please see
http://www.open-mpi.org/community/lists/announce/2014/08/0063.php

I also simplified the Fortran dependency, as the help message doesn't seem to add useful information.
Oh that's right, sorry about that. I'll change it back.