Revise task exit log messages from slurmstepd to be clearer,
and include the termination signal if WIFSIGNALED, and a
message "(core dumped)" if a corefile was generated. The
extra timestamp is also removed.

  event that the hardware does not match the configuration information.

This patch abstracts the establishment of slurm user credentials
in slurmctld when SlurmUser != root. It adds a call to setgid()
to adopt the SLURM user's primary group, instead of running with
whatever primary group was in effect when invoking the slurmctld
executable. Also, errors in establishing user credentials are
fatal errors, instead of just warnings.

This is a minor security enhancement.

This patch adds a spank plugin hook that is called just after
fork() within each task, but before elevated privileges have
been dropped. This allows plugins to run privileged actions
on a per-task basis, which wasn't possible with the existing
task_init hook called just before exec.

nodes in the default partition used for testing

    --cpus-per-task option not properly handled.

   honor the exclusive but for one CPU per task.