Support for both INNER JOIN and LEFT JOIN

Eg:

    $builder
        ->from('FooBundle:Message', 'm')
        ->innerJoin('m.conversation', 'c')
        ->leftJoin('m.senderUser', 'su')
        ->leftJoin('m.senderGuest', 'sg')

Legacy join method still works

    $builder
        ->from('FooBundle:Message', 'm')
        ->join('m.conversation', 'c')
        ->join('m.senderUser', 'su')
        ->join('m.senderGuest', 'sg')

will give LEFT JOINS as before.