UPDATE 2-Brent slips to $110, set for weekly rise

* Brent, WTI set for second weekly gain in three * Fed taper affirms improved U.S. economic outlook, fuel demand * Libya crude exports fall to 110,000 bpd (Updates prices) By Florence Tan SINGAPORE, Dec 20 (Reuters) - Brent crude slipped to $110 a barrel on Friday, but was heading for its second weekly gain in three, buoyed by Libyan supply cuts and a rosy outlook for fuel demand in the United