Case C-346/06: Judgment of the Court (Second Chamber) of 3 April 2008 (reference for a preliminary ruling from the Oberlandesgericht Celle (Germany)) — Dirk Rüffert, in his capacity as liquidator of the assets of Objekt und Bauregie GmbH & Co. KG v Land Niedersachsen (Article 49 EC — Freedom to provide services — Restrictions — Directive 96/71/EC — Posting of workers in the context of the provision of services — Procedures for the award of public works contracts — Social protection of workers)