When Dieter Zetsche, Daimler’s chief executive, held alliance talks with BMW last year, he floated the idea of a cross-shareholding with his company’s German rival. His request was spurned by BMW and its controlling family shareholders, the Quandts, who saw themselves as stronger than Daimler. A year later, Daimler has a new possible alliance partner in Renault, a company in weaker financial shape than…