Jetpack Dependencies: Errors on child themes

The WordPress.org version 1.2.4 of Goran was throwing the following error:

`Cannot redeclare class Edin_Theme_Plugin_Enhancements in /srv/www/wordpress-trunk/wp-content/themes/edin/inc/plugin-enhancements.php on line 10`

The issue appears to be related to both Goran and Edin including Edin's plugin-enhancement.php file, causing the class Edin_Them_Plugin_Enhancements twice.

We need a way to make sure the script 'knows' a theme is a child theme, and does not cause the class to be declared twice (possibly by adding a check to see if it's already declared, or by using `require_once` to add the file).