WRAPUP 4-Olympics-Dibaba aims for double, doping cases reported (Reuters)

* Ethiopian Dibaba aims for track double in 5,000m * Two doping cases surface, accusations fly * Spice Girls to perform at closing ceremony * Jamaica eyes relay sprint golds after Bolt heroics (Adds BMX results, Rogge comments) LONDON, Aug 10 (Reuters) - Ethiopian Tirunesh Dibabaattempts a track double on Friday in the 5,000 metres to add tothe 10,000 Olympic crown she retained in thrilling fashion aweek ago in London, but two doping cases overshadowed anotheraction-packed day at the Games. ...