sacctmgr to accept "PU" suffix in addition to "PerUser"

sacctmgr output used a suffix of "PU" for per user, but only
  accepted input with a suffix of "PerUser". The output all
  used a suffix of "PU". The code has been modified to accept
  both sufficies (e.g. MaxJobsPerUser=# or MaxJobsPU=#).