Previous commit f2794740 reverts Nathans changes. However it turns out
that I was unable to trace his logic until I started investigation of
icsplit hang. Bug was triggered when splitting Intercom was giving a group
where on side of the communicator was empty (icsplit, intercom create #2).
in this case remote_size == 0 and there is no way to distinguish between
inter- and intra-communicator.
Conclusion: We do need to distinguish between intra- and inter-communicators.
So we should use ompi_mpi_group_null.group.
7690f4027a