error messages telling the user to use salloc, sbatch, and sattach,
respectively (rather than just saying "unrecognized option").

options.

That functionality is now available in salloc, sbatch, and sattach,
respectively.

Also removed the forked message process from srun.  The slurmctld will no
longer kill a job allocation just because it cannot ping srun, so it
is no longer critical to keep a message process running when the user
stops the srun process.

This lets us examine the files to help determine what happened.