thorium: make sure that the number of transport implementations is not 0

Link: https://github.com/GeneAssembly/biosal/issues/834
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use MPI 1 point-to-point on Cray systems

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use MPI 1 two-sided nonblocking comm. on Blue Gene/Q

Link: https://github.com/GeneAssembly/biosal/issues/834
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>