NEW YORK (Reuters) - Oil prices resumed a three-week downturn on Thursday as swelling world crude supplies eclipsed lingering concerns over thin heating oil stocks in the United States, Europe and Asia. U.S. light crude futures (CLc1: Quote, Profile, Research) settled down 62 cents at $46.22 a barrel, cutting into Wednesday's 73 cent advance. London Brent (LCOc1: Quote, Profile, Research) was down four cents at $42.72. The losses came after producer group OPEC revised down its expectations of oil demand growth for next year and projected a rare big winter stock build if the group keeps producing at current levels....