Included Mage.php for Mage_Core_Model_Factory class not found

See issue #1 

This core bug causes the impossibility to set to false the `$_includeMage` property, because the original `require_once` of Mage.php is done inside the `if` that evaluate such property. This cause a fatal error trying to instantiate the `Mage_Core_Model_Factory` because the autoloader is initialized inside Mage.php.