gang scheduling module. Make identification of preemptable jobs an argument
    to the select_g_job_test function rather than calling preempt plugin from
    the select plugin. Make output of srun --test-only option include a list
    of preempted job IDs. 
    svn merge -r18780:18815 https://eris.llnl.gov/svn/slurm/branches/preempt.job.list