Cron and Batch utilities

[jgarzik]

Implement cron and batch-related utilities:

• [ ] cron daemon. While not specified, its need is implied and worth building.
• [ ] at
• [ ] batch
• [ ] crontab
• [ ] qalter
• [ ] qdel
• [ ] qhold
• [ ] qmove
• [ ] qmsg
• [ ] qrerun
• [ ] qrls
• [ ] qselect
• [ ] qsig
• [ ] qstat
• [ ] qsub