Update index.php

__DIR__ The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(__FILE__). This directory name does not have a trailing slash unless it is the root directory. (Added in PHP 5.3.0.)

if ( ! defined('KOHANA_START_TIME'))
if ( ! defined('KOHANA_START_MEMORY'))

Why this check? and why not the same for APPPATH, MODPATH, ..?