Relax statement type declaration

fetch() is part of the ResultStatement interface. Using Statement as a
type declaration needlessly constrains people to use this class only
with implementations of Statement.

lib/Doctrine/DBAL/Driver/StatementIterator.php

@@ -6,10 +6,10 @@ use IteratorAggregate;
 
 class StatementIterator implements IteratorAggregate
 {
-    /** @var Statement */
+    /** @var ResultStatement */
     private $statement;
 
-    public function __construct(Statement $statement)
+    public function __construct(ResultStatement $statement)
     {
         $this->statement = $statement;
     }