MPI support: add support for spectrum-mpi

[mikebentley15]

The spectrum-mpi product is a production-quality implementation of MPI from IBM. See this page for more information. FLiT has not been tested with spectrum-mpi yet. I am guessing that just because we support OpenMPI does not automatically mean that we support spectrum-mpi. It would be worthwhile to investigate how much functionality already works and how much needs to be done to officially support it.