Change weird way of adding an entry to SplObjectStorage

lib/Doctrine/DBAL/Schema/Visitor/DropSchemaSqlCollector.php

@@ -80,8 +80,7 @@ class DropSchemaSqlCollector extends AbstractVisitor
             throw SchemaException::namedForeignKeyRequired($localTable, $fkConstraint);
         }
 
-        $this->constraints->attach($fkConstraint);
-        $this->constraints[$fkConstraint] = $localTable;
+        $this->constraints->attach($fkConstraint, $localTable);
     }
 
     /**