job_event: always hibernate a jobs event handler after after it is done

This process will still be accessed occusionally when the user needs it,
however, we want to consume as little memory as possible for this process.
test: move test_pickle to the python unittest directory
dPickle: avoid using a custom pickler for partial functions python>2.6
job_event: handle the non-empty dirty buffer when event file is closed
Merge pull request #565 from pooya/je_hibernate

implement hibernation for job event handler processes