bug-fix: trying to eliminate deadlocks

- when assignment_manager attempts to complete and assignment,
  it identifies any adjudications and sets the adjudicate column
  of the assignment's and its sibling's test_entry records, which
  can lead to a deadlock if the sibling is currently being worked on.
  Add create and release semaphore bracketing the adjudication loop.
- security enhance: use database_class format on an id in the sql query
  that deletes adjudicate test_entry daughter records