[Dovecot] Thunderbird can't see a maildir named .Inbox (yeah I know, poor name)

[Adam McDougall]

I discovered by chance while migrating some user email to dovecot,
one of them had a mailbox called "Inbox" and my script migrated it to
a Maildir called .Inbox but Thunderbird could not see it at all, even in
subscription lists.  I tested with my account and it looks like mutt CAN
see it.  This seems like a client issue so I'll just make my migration 
script
rename anything called Inbox to avoid it, but I thought I would send a note
incase anyone else trips on it.