suzerain: new-style 'use mpi'

I suspect this difference is causing linking issues on
the PECOS compute cluster with OpenMPI.  And there's
no reason not to use the newer style import as I'm
not targeting bizarro IBM XL Blue Gene stuff.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44146 0bd85f0b-c151-43b9-a1e9-27231104551f