Bug#826543: cupsd fails to remove job files at end of PreserveJobFiles interval

[Sergio Gelato <Sergio.Gelato@astro.su.se>]

I've now tested my proposed change and played with LogLevel debug2.
The change doesn't seem to do any harm but it didn't obviously cure
the problem either. It took several daemon restarts (and one access
to the web interface, though I'm not sure that was the trigger) for
expired job files to be removed.

I'll keep monitoring the situation, although I'm now running with
PreserveJobFiles Off since that seems better for privacy.