Use more flexible mechnanism to find json installation.

Fix srun from inheriting the SLURM_CPU_BIND and SLURM_MEM_BIND environment variables when running in an existing srun (e.g. an srun within an salloc).

Bug 1888

of Knight's corner.

Conflicts:
	src/slurmctld/job_mgr.c

At the start of a scheduling cycle, the job's "reason" field can
be cleared. If the scheduler fails to reach that job and set its
value to a new reason, the original reason was lost and the state
reports would report NoReason. This change saves the last reason
for a job being in a pending state and reports that value to the
user until we have a new valid reason for it still being in a
PENDING state.
bug 1919

Conflicts:
	contribs/pmi2/testpmi2.c
	src/slurmctld/node_scheduler.c

bug 1920

Improve job state reason string when required nodes not available.
bug 1920

bug 1915

bug 1914

Desired for MPI support

when looking for CR_CORE_MEMORY)

If the pre_run API fails (after job allocation has been made), then
  release the resource and requeue/hold the job

The "paths" API is returning an error in some cases when it should
not, this adds logic to test the response string and process the
paths file produced when it actually does work.

bug 1911

Remove our work around for a bug in the Cray API that has recently
  been fixed.
Improve error message for root jobs trying to use DW.

One API was fixed, another broke (work around for one removed, added
for the other API).

This fixes some race conditions with threads (e.g. a buffer is found
to be missing before the thread tearing it down records the operation
has completed).

If the show_sessions/instances/configuration API returns an error
code, test its contents before trying to parse it since it may
contain some genuine error message. This provides a better work
around for bug already reported to Cray.