Check for the binding policy used. We are only interested in
whether mapby-node has been set right now (could be extended later)
and only on MPI_COMM_WORLD, since for all other sub-communicators
it is virtually impossible to identify their layout across nodes
in the most generic sense. This is used by OMPIO for deciding which
ranks to use for aggregators
Signed-off-by: Edgar Gabriel <gabriel@cs.uh.edu>
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