 Citro?ns used to be the most glamorous, technically advanced cars on the road - so distinctive that in the Forties and Fifties their extravagant engineering and flamboyant styling made them the choice of high-rollers and heads of state. Then in the 1980s the French car maker lost its panache, and only now are its derring-do and audacity returning, as embodied by the world's first mass-produced, purpose-built, diesel-electric hybrid car.  Launched last week at the Shanghai motor show, in a country where hybrids and electric cars are much in demand to address choking pollution, the new DS5 takes on the BMW 3-series and Mercedes-Benz C-class with the same upstart attitude of its smaller DS3 sibling.  The DS5's bold styling stands out in an  