[horde] listFolders function for vfs file backend

[Chuck Hagenbuch]

Quoting Liam Hoekenga <liamr at umich.edu>:

> Borrowed heavily from the FTP backend.... it seems to work ok - eg the
> "move / copy to" folder list in Gollem works now when using the VFS
> "file" driver:
> 
>      http://www.umich.edu/~liamr/horde/vfs-file-listFolders.diff

Committed, thanks.

-chuck

--
Charles Hagenbuch, <chuck at horde.org>
I know there's fish out there, but where g-d only knows.