allow use of Torque per-job temporary directories

Torque can be configured to create a per-job temporary directory that will automatically be cleaned up at the completion of a Torque job. At our site, we are strongly encouraged to use this directory and not /tmp. The name of the per-job temp dir is in the environment variable TMPDIR in the Torque job's environment. It would be very useful for HOD to be extended so that one could write in hodrc:

[ringmaster]
temp-dir = $TMPDIR
work-dirs = $TMPDIR/1

[hodring]
temp-dir = $TMPDIR

such that $TMPDIR is evaluated inside the Torque job.