to see the bug it seems to be triggering in the forwarding code.

for all nodes.  This will allow us to use tree communication for the
reattach RPC in sattach.

The srun, sbatch, and salloc --exclusive options now just set
"shared=0", and --shared sets "shared=1".  The second exclusive
variable appeared to be redundant.

Add --usage to sattach to quiet test16.1.

More command line option trimming.