Cycling-Hammer steers U.S. to gold, Dibben roared to title

* Americans claim their first women's team pursuit gold * Britain's Dibben snatches points race title from Graf * Italy's Ganna win the men's individual pursuit * Russia's Voinova retains her 500m time trial title (Adds points race winner) By Martyn Herman LONDON, March 4 (Reuters) - Sarah Hammer led the U.S. to their first gold medal in women's team pursuit before Britain's Jonathan Dibben produced a thrilling climax to day three of the world track championships in the points race on Friday. Th