Last changed: September 18, 2012 1:30PM By JOE McDONALDAssociated PressBEIJING (AP) -- China filed a World Trade Organization case Monday challenging U.S. anti-dumping measures on billions of dollars of kitchen appliances, paper and other goods, adding to worsening trade strains as global demand weakens.Beijing's move came shortly before the Obama administration filed its own WTO case accusing Chi