NOTE: see option.h bootrun

- option.h: new line option rebootreset = as 'volatile' but from system reboot and not fcron's restart
- option.h: new line option runonce = do not reschedule after having run once
- fileconf.c able to parse vixie cron's '@reboot command' = '&bootrun,runonce * * * * big-period' 
- fcron starts -> check reboot lock -> sets system-reboot var to 0 or 1
- when fcron loads config: if cl->option rebootreset and system-reboot => do as volatile 
- when scheduling a job, check runonce: if set, do not reschedule

DOC
- @reboot supported
- anacron job emulated correctly
- 
