METALS-Aluminium drops for third session on rising stockpiles, nickel up

(Updates prices) By Manolo Serapio Jr MANILA, May 18 (Reuters) - London aluminium futures slipped for a third straight session on Friday as inventories increased, easing worries over a supply shortage in the aftermath of U.S. sanctions on major Russian producer Rusal. On-warrant aluminium stocks in warehouses certified by the London Metal Exchange - inventories that are not earmarked for delivery - surged by 153,075 tonnes or 18 percent on Wednesday, LME data showed on Thursday. &lt