change to config file missing from rev1580 (#1485179)

config/main.inc.php.dist

@@ -91,8 +91,8 @@ $rcmail_config['smtp_helo_host'] = '';
 $rcmail_config['smtp_log'] = TRUE;
 
 // these cols are shown in the message list
-// available cols are: subject, from, to, cc, replyto, date, size, encoding
-$rcmail_config['list_cols'] = array('subject', 'from', 'date', 'size');
+// available cols are: subject, from, to, cc, replyto, date, size, encoding, flag
+$rcmail_config['list_cols'] = array('subject', 'from', 'date', 'size', 'flag');
 
 // includes should be interpreted as PHP files
 $rcmail_config['skin_include_php'] = FALSE;