[index] Use constant WHITELIST_FILE all the way

index.php

@@ -71,7 +71,7 @@ if(!is_writable(CACHE_DIR))
 	die('RSS-Bridge does not have write permissions for ' . CACHE_DIR . '!');
 
 // Check whitelist file permissions (only in DEBUG mode)
-if(!file_exists('./whitelist.txt') && !is_writable('./'))
+if(!file_exists(WHITELIST_FILE) && !is_writable(dirname(WHITELIST_FILE)))
 	die('RSS-Bridge does not have write permissions for ' . WHITELIST_FILE . '!');
 
 // FIXME : beta test UA spoofing, please report any blacklisting by PHP-fopen-unfriendly websites