Fix: Bad path for some includes

ChangeLog

htdocs/admin/mails.php

htdocs/comm/mailing/fiche.php

htdocs/comm/propal.php

htdocs/commande/fiche.php

htdocs/compta/facture.php

htdocs/core/class/commonobject.class.php

htdocs/fourn/commande/fiche.php

htdocs/includes/triggers/interface_all_Demo.class.php-NORUN

htdocs/install/mysql/data/llx_c_actioncomm.sql

htdocs/install/mysql/migration/2.8.0-2.9.0.sql

htdocs/langs/en_US/commercial.lang

htdocs/langs/fr_FR/commercial.lang