14.1.2 Changes from `'mark' folder to `'flag'.

The folder `'mark' will be automatically converted to `'flag' folder when you first start the new version of Wanderlust. But there are some restrictions on this type of migrated folder.

1. `important' flag attached will not be removed by deleting the associated message in `'flag' folder.

2. The message won't be deleted by removing `important' flag in `'flag' folder.

3. help-echo will not show you the old message.

If you have problem with migrating from `'mark' folder to the `'flag' folder, invoking M-x elmo-global-mark-upgrade will transfer the message from `'mark' folder to the `'flag' folder. The duplicated message will not be processed, you may issue that command repeatedly.