title: symfony 1.4.15 bug with php 7
body: <p>I'm migrating my project made from symfony 1.4.15 with doctrine (1.2 i guess) using PHP&lt;5 to PHP7 and i have big problems: </p>
  
  <p>When i'm doing :</p>
  
  <pre><code>-&gt;select('k.*,v.*,t.*')
  -&gt;from('DataKey k')
  -&gt;leftJoin('k.Values v')
  </code></pre>
  
  <p>with config : </p>
  
  <pre><code>DataKey:
     columns:
       type:                { type: string(5), notnull: true, comment: 'Type de donnée (list/int/text/float)' }
       description:         { type: string(255), notnull: true, comment: 'Libelle' }
       unit:                { type: string(10), notnull: false, comment: 'Unité de valeur' }
  
  DataValue:
    columns:
       key_id:              { type: integer, notnull: true, comment: 'Identifiant de donnée' }
       value_id:            { type: string(10), notnull: true, comment: 'Identifiant de valeur' }
       description:         { type: string(255), notnull: true, comment: 'Libelle' }
    relations:
       DataKey:            { class: DataKey, local: key_id, foreign: id }
  </code></pre>
  
  <p>i got this error :</p>
  
  <p>/doctrine/Doctrine/Relation.php on line 451
  PHP message: 
  PHP Notice:<br>
  Array to string conversion in /lib/vendor/symfony/lib/plugins/sfDoctrinePlugin/lib/vendor/doctrine/Doctrine/Relation.php on line 451</p>
  
  <p>PHP message: Unknown record property / related component "<pre>
  alias : DataKey
  foreign : id
  local : key_id
  class : DataKey
  type : 0
  table : Object(DataKeyTable)
  localTable : Object(DataValueTable)
  name : 
  refTable : 
  onDelete : 
  onUpdate : 
  deferred : 
  deferrable : 
  constraint : 
  equal : 
  cascade : Array
  owningSide : 
  refClassRelationAlias : 
  foreignKeyName : 
  orderBy : 
  </pre>" on "DataValue"</p>
  
  <p>Any ideas? </p>