Fix entities returning duplicates

[PabstMirror]

Fix #567

@commy2
Not sure if there is a better way to do this.
arrayIntersect is expensive on very large arrays, but addClassEH is probably only going to be called at init.

[commy2]

arrayIntersect is fine once on addClassEventHandler. We are doing this in the release version already with entities + allUnits, so it's still an improvement over all after the update.