Support daemonizing of delayed_job_celluloid

This is an amazing find for me! We have been struggling with DJ memory usage for months, trying everything, including stripping out Rails components in the DJ load sequence. We hope to get this working with 10 threads, so our memory usage will be a lot less than 2Gb, so we can replace our existing background job script!

Unfortunately, I could not get Minitest to work with the existing tests... even after switching to `Klass < Minitest::Test`. Which version of minitest are you using? Might have to leave this for another day.

Cheers,
Nigel