This fixes a problem reported by @bgoglin where rank-by was incorrectly generating values when ranking by a type of object (e.g., socket). It also corrects the handling of the pernode, npernode, and npersocket options - these should only set the #procs and the default mapping pattern. They specifically should not prohibit the user from requesting a different mapping.
Thus, the following should be valid:
mpirun -npernode 2 --map-by socket ...
should put 2 procs on each node, mapping them by-socket on each node.
Signed-off-by: Ralph Castain <rhc@open-mpi.org>