Fix issue with associations attached to a specific partition with no other association, and requesting a different partition.

Fixed issue where assoc_mgr cache wasn't always loaded correctly if the slurmdbd wasn't running when the slurmctld was started.

Fixed issue where if a system has unset messages to the dbd in 2.1 and upgrades to 2.2.  Messages are now processed correctly now.

    minimize lost messages. Effects slurmd epilog complete messages and PMI
    key-pair transmissions. Patch from Gerrit Renker, CSCS.

    when job preemption is configured.

    job_submit and job_modify functions as an error and the user request should
    be treated as an error.

    into an array. Patch from Gerrit Renker, CSCS.