Revert mysqli changes.

I don't really understand the mysqli driver too much and the changes
break the tests so undo using an iterator for this particular driver.

lib/Doctrine/DBAL/Driver/Mysqli/MysqliIterator.php

-<?php
-
-namespace Doctrine\DBAL\Driver\Mysqli;
-
-use Doctrine\DBAL\Driver\AbstractIterator;
-
-class MysqliIterator extends AbstractIterator implements \Iterator
-{
-    protected function fetch()
-    {
-        switch ($this->defaultFetchMode) {
-            case \PDO::FETCH_COLUMN:
-                return $this->fetchColumn();
-            default:
-                return $this->fetch($this->defaultFetchMode);
-        }
-    }
-}

lib/Doctrine/DBAL/Driver/Mysqli/MysqliStatement.php

@@ -406,6 +406,8 @@ class MysqliStatement implements \IteratorAggregate, Statement
      */
     public function getIterator()
     {
-        return new MysqliIterator($this->_stmt, $this->_defaultFetchMode);
+        $data = $this->fetchAll();
+
+        return new \ArrayIterator($data);
     }
 }