Properly requeue jobs for resubmissions of IDs in active state

We want the property that only one instance of a job with a given ID is
executing at a certain time.

Before this commit, if a job was submitted while a job was in the active
state, it could be run simultaneously with the currently running one.

This prevents the case where two jobs with the same ID might be
interleaved.
Merge pull request #18 from incredible-labs/active_requeue

Properly requeue jobs for resubmissions of IDs in active state