Improve UPDATE_JOBAD handling in the schedd. #3909

* In SetAttribute(), don't send signals for jobs already in the
  DirtyJobIDs list.
* In SetAttribute(), don't send signals to pids that have been signaled
  recently.
* Don't send signals for local or standard universe jobs.
* During the periodic notification, if a shadow/gridmanager pid can't be
  found, mark the job as clean and remove it from the DirtyJobIDs list.