Don't rely on include_path to include files.

Always use dirname() or, once available, ABSPATH.

props ketwaroo, hakre.
fixes #17092.


git-svn-id: https://develop.svn.wordpress.org/trunk@25616 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/ms-admin.php

@@ -7,7 +7,7 @@
  * @since 3.0.0
  */
 
-require_once( './admin.php' );
+require_once( dirname( __FILE__ ) . '/admin.php' );
 
 wp_redirect( network_admin_url() );
 exit;