OpObjectExtraction: Fixed typo in exception format string.
(Investigating #521)
ObjectExtraction: Changed an Exception into a DatasetConstraintError.
(Still investigating #521)
ThreadRouter: Assert if the @threadRouted function attempts to return a value.
DataSelection: Fixed a bug that caused dataset repairs to always fail (@threadRouted functions can't return a value!)
Tracking: Check constraints of each dataset immediately when it becomes ready().
Fixes #521