Fix: possibility to have more hooks in the same page

htdocs/comm/propal.php

htdocs/comm/propal/class/propal.class.php

htdocs/commande/class/commande.class.php

htdocs/commande/fiche.php

htdocs/compta/facture.php

htdocs/compta/facture/class/facture.class.php

htdocs/core/class/commonobject.class.php

htdocs/core/tpl/freeproductline_create.tpl.php

htdocs/core/tpl/predefinedproductline_create.tpl.php

htdocs/lib/pdf.lib.php

htdocs/main.inc.php