Prevent clearing reason field for pending jobs.

This bug was introduced in commit f1cf6d2df1abbcf2703e5ba81bc4792487a691d8
fix for bug 290
BLUEGENE - remove duplicate definition
BGQ - Fix issue with preemption on sub-block jobs where a job would kill
all preemptable jobs on the midplane instead of just the ones it needed to.
Remove vestigial function definition, correct log messages

job_step_cancel() appears to have been renames job_step_signal()
at some point in the past.
Clarify documentation for node reboot logic
Merge branch 'slurm-2.5'

Conflicts:
	src/slurmctld/job_scheduler.c