This dir contains dirs with a list of currently being processed filtergrams.
the list is file names where the name is FSN.  The files are empty
and are removed when each queued job finishes.  When the
controlling script is done submitting jobs to the queue it waits until
all FSN filename are gone then removes the control dir.  The
control dir name is the hostname of the machine running the top
level control script and the PID on that machine.