Update DocumentUserProvider to implement the new UserProviderInterface
Update DocumentUserProvider to implement the new UserProviderInterface

Breaks compatibility with Symfony2beta4

0mars/DoctrineMongoDBBundle,doctrine/DoctrineMongoDBBundle,alcaeus/DoctrineMongoDBBundle,sarcher/DoctrineMongoDBBundle,malarzm/DoctrineMongoDBBundle,Soullivaneuh/DoctrineMongoDBBundle,alcaeus/DoctrineMongoDBBundle,tomasbro/DoctrineMongoDBBundle,Soullivaneuh/DoctrineMongoDBBundle,jahller/DoctrineMongoDBBundle,juchi/DoctrineMongoDBBundle,jahller/DoctrineMongoDBBundle,0mars/DoctrineMongoDBBundle,juchi/DoctrineMongoDBBundle,castarco/DoctrineMongoDBBundle,castarco/DoctrineMongoDBBundle,tomasbro/DoctrineMongoDBBundle,malarzm/DoctrineMongoDBBundle,stof/DoctrineMongoDBBundle