Update lib/Doctrine/ORM/EntityRepository.php

simply permit an indexby directly from the repo object

Ex : 
#Acme\AcmeBundle\Repository
#Before
public function findAllIndexById(){
    $qb = $this->_em->createQueryBuilder()
                    ->select('root')
                    ->from('Acme', 'root', 'root.id');
    /*...*/
}

#After
public function findAllIndexById(){
    $qb = $this->createQueryBuilder('root','root.id');
    /*...*/
}