Prepare fix to hide images generated by "preview" feature.

htdocs/adherents/document.php

htdocs/comm/action/document.php

htdocs/comm/propal/document.php

htdocs/commande/document.php

htdocs/compta/deplacement/document.php

htdocs/compta/facture/document.php

htdocs/compta/sociales/document.php

htdocs/contrat/document.php

htdocs/core/ajax/ajaxdirpreview.php

htdocs/core/class/html.formfile.class.php

htdocs/core/lib/files.lib.php

...e/modules/project/pdf/doc_generic_project_odt.modules.php

...modules/project/task/pdf/doc_generic_task_odt.modules.php

htdocs/ecm/class/ecmdirectory.class.php

htdocs/ecm/docmine.php

htdocs/ecm/search.php

htdocs/fichinter/document.php

htdocs/fourn/commande/document.php

htdocs/fourn/facture/document.php

htdocs/install/repair.php