Fix for #384. Check relationships in Entity::_isset().
Fix for #384. Check relationships in Entity::_isset().

whowgames/lithium,UnionOfRAD/lithium,jails/lithium,davidpersson/lithium,qoqa/lithium,SensCritique/lithium,graphis/lithium,davidpersson/lithium,pixelcog/lithium,wbeater/lithium,m4rcsch/lithium-core-library,mehlah/lithium,muyehub/lithium,graphis/lithium,wbeater/lithium,UnionOfRAD/lithium,mehlah/lithium,whowgames/lithium,qoqa/lithium,m4rcsch/lithium-core-library,pixelcog/lithium,muyehub/lithium,SensCritique/lithium,datachand/lithium,datachand/lithium,jails/lithium