imap4d virtual domains

[Jakob 'sparky' Kaivo]

OK, I said it should be fairly easy to add the pop3d virtual domain
code to imap4d, and it was. It seems to work nicely with two issues:

1) When I list mailboxes, I now get two INBOX folders.
2) It will take a little more looking into the RENAME function to get
   that right, I left it as-is for now, which means it will behave in
   an unknown manner if a virtual domain user tries to rename INBOX.

Please test and enjoy.

-- sparky