Fix: Pb with the token post protection

htdocs/main.inc.php

@@ -185,7 +185,7 @@ if (empty($conf->global->MAIN_FEATURES_LEVEL))	// Check validity of token, only
 		if (($_POST['token'] != $_SESSION['token_level_1']) && ($_POST['token'] != $_SESSION['token_level_2']))
 		{
 			dol_syslog("Invalid token in ".$_SERVER['HTTP_REFERER'].", action=".$_POST['action'].", _POST['token']=".$_POST['token'].", _SESSION['token_level_1']=".$_SESSION['token_level_1'].", _SESSION['token_level_2']=".$_SESSION['token_level_2']);
-			print 'Unset POST by CSRF protection in main.inc.php.';
+			//print 'Unset POST by CSRF protection in main.inc.php.';	// Do not output anything because this create problems when using the BACK button on browsers.
 			unset($_POST);
 		}
 	}