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

(as requested in #2050)
diff --git a/system/database/drivers/mysql/mysql_result.php b/system/database/drivers/mysql/mysql_result.php
index a6dcde4..293980e 100644
--- a/system/database/drivers/mysql/mysql_result.php
+++ b/system/database/drivers/mysql/mysql_result.php
@@ -149,7 +149,7 @@
 	 * @param	int	$n
 	 * @return	bool
 	 */
-	protected function _data_seek($n = 0)
+	public function data_seek($n = 0)
 	{
 		return $this->num_rows
 			? @mysql_data_seek($this->result_id, $n)