Add support for e-mail notification on job state changes.

NEWS

doc/man/man1/srun.1

slurm/slurm.h.in

src/common/slurm_protocol_defs.c

src/common/slurm_protocol_pack.c

src/slurmctld/agent.c

src/slurmctld/agent.h

src/slurmctld/job_mgr.c

src/slurmctld/node_scheduler.c

src/slurmctld/slurmctld.h

src/srun/allocate.c

src/srun/opt.c

src/srun/opt.h