FIX invoice creation : use dol_include_once instead of require_once to allow external modules.

[thomas-Ngr]

Fix : Impossible to create a supplier invoice from an object introduced by an external module

Loading the class of the origin element should be done through dol_include_once and not require_once, to allow use from external modules.

This is right on most cards:

• compta/facture/card.php
• comm/propal/card.php
• commande/card.php
• fourn/commande/card.php
• fourn/propal/card.php

.. but not on fourn/facture/card.php

[rycks]

as it's already done on other cards it's ok for me