Flag task processing on task submission.

Task proxies are supposed to spawn once they achieve the 'submitted'
state, but the flag for a pass through the main task processing loop
(including spawning) was not being set on this state, which meant
submitted tasks would not spawn immediately if nothing else was
happening. Test: a single cycling task that submits to a non-active
queue (e.g. 'at' job submission with atd turned off) should submit
out to the runahead limit without requiring any suite nudging.
Merge pull request #690 from hjoliver/task-proc-on-submit

Flag task processing on task submission.