Need to include files.php to use sq_is_writable()

src/configtest.php

@@ -87,6 +87,7 @@ define('SM_PATH', '../');
 require(SM_PATH . 'include/constants.php');
 require(SM_PATH . 'functions/global.php');
 require(SM_PATH . 'functions/strings.php');
+require(SM_PATH . 'functions/files.php');
 $SQM_INTERNAL_VERSION = explode('.', SM_VERSION, 3);
 $SQM_INTERNAL_VERSION[2] = intval($SQM_INTERNAL_VERSION[2]);