"BASEPATH check" consistency

As described in issue #2870

+ A change in the „How to create a library” example in the user_guide
diff --git a/application/config/config.php b/application/config/config.php
index e0b5a4c..ae89715 100644
--- a/application/config/config.php
+++ b/application/config/config.php
@@ -1,4 +1,4 @@
-<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
+<?php
 /**
  * CodeIgniter
  *
@@ -24,6 +24,7 @@
  * @since		Version 1.0
  * @filesource
  */
+defined('BASEPATH') OR exit('No direct script access allowed');
 
 /*
 |--------------------------------------------------------------------------