Rename DB_result _data_seek() to data_seek() and make it publicly available

(as requested in #2050)
diff --git a/system/database/drivers/mysqli/mysqli_result.php b/system/database/drivers/mysqli/mysqli_result.php
index d55188e..ac0f1a8 100644
--- a/system/database/drivers/mysqli/mysqli_result.php
+++ b/system/database/drivers/mysqli/mysqli_result.php
@@ -136,7 +136,7 @@
 	 * @param	int	$n
 	 * @return	bool
 	 */
-	protected function _data_seek($n = 0)
+	public function data_seek($n = 0)
 	{
 		return $this->result_id->data_seek($n);
 	}