When we requeued the task, the `notbefore` date was calculated relative
to the MySQL clock and this is out of sync with PHP's clock. So it was
setting `notbefore` to the past and the job would just get run over and
over again. Now the dates calculated are all by PHP
Merge pull request #8 from rgmccaw/fix_date_discrepancy_for_requeueing_tasks

When we requeued the task, the `notbefore` date was calculated relative