[DoctrineBundle] made tweaked an error message

src/Symfony/Bundle/DoctrineBundle/Security/EntityUserProvider.php

@@ -26,7 +26,7 @@ class EntityUserProvider implements UserProviderInterface
             $user = $this->repository->findOneBy(array($this->property => $username));
         } else {
             if (!$this->repository instanceof UserProviderInterface) {
-                throw new \InvalidArgumentException('The Doctrine user manager must implement UserManagerInterface.');
+                throw new \InvalidArgumentException(sprintf('The Doctrine repository "%s" must implement UserProviderInterface.', get_class($this->repository)));
             }
 
             $user = $this->repository->loadUserByUsername($username);