New: A module can force theme directory

htdocs/main.inc.php

@@ -868,7 +868,9 @@ function top_htmlhead($head, $title='', $disablejs=0, $disablehead=0, $arrayofjs
 
         print '<!-- Includes for Dolibarr, modules or specific pages-->'."\n";
         // Output style sheets (optioncss='print' or '')
-		print '<link rel="stylesheet" type="text/css" title="default" href="'.DOL_URL_ROOT.$conf->css.'?lang='.$langs->defaultlang.'&theme='.$conf->theme.(! empty($_GET["optioncss"])?'&optioncss='.$_GET["optioncss"]:'').'">'."\n";
+        $themepath=dol_buildpath((empty($conf->global->MAIN_FORCETHEMEDIR)?'':$conf->global->MAIN_FORCETHEMEDIR).$conf->css,1);
+        //print 'themepath='.$themepath;exit;
+		print '<link rel="stylesheet" type="text/css" title="default" href="'.$themepath.'?lang='.$langs->defaultlang.'&theme='.$conf->theme.(! empty($_GET["optioncss"])?'&optioncss='.$_GET["optioncss"]:'').'">'."\n";
 		// CSS forced by modules (relative url starting with /)
 		if (is_array($conf->css_modules))
 		{