I just fixed it in defb7d57
together with two other missing occurrences of the config_cascade.
There are still two occurrences which probably need to be fixed, both in the beginning of ./_test/index.php. As I don't know much about those tests, I didn't change it. I wasn't sure if the config_cascade is already available at that point? And it also seems partly wrong that the "if(!defined('DOKU_CONF'))" is missing before the definition of DOKU_CONF. In case there's a reason for it, there's no point in changing that instant to use the config_cascade anyway.