Fixes:
	The auto-retrain option. This function is fully working now. The
classifiers are only queued for retraining only if the GPSystem object
is not already retraining that classifier.

Adds:
	The "UniqueBlockingQueue" class which makes auto-retrain functional.

Changes:
	Changes the Job class by overriding the "equals" function. This
function is necessary for queueing unique jobs on the GPSystem.