Overhaul the command line parsing code to handle #SBATCH arguments in
  batch scripts.

Remove unnecessary multi-prog option (multi-prog is slaunch-only).

code from test18.14.

with and associated launcher.  A batch script only has job allocation-specific
variables set.

Add new SLURM_JOB_* environment variables.

variables are missing.

in the spec file did not have any parameters.

Also, no need to sift through environment variables for the task's ID,
the slurmstepd already knows that.

There appears to be a bug in slurmstepd's task_exec.c parsing of the
multi-prog script when commands have no command line parameters.

srun is also broken in this respect, it is not slaunch specific.

honoring the overcommit flag.

The "--threads" option is now named "--pmi-threads", since it only applies
to PMI threading.  At this time slaunch has no other threading which might
requiring throttling.

made step_spec->overcommit 0 out cpu_count when creating a step so we don't check for avaliable processors. making it overcommit

Fix batch environment variable setting.