IMAP RENAME: If dest mailbox exists but source doesn't, fail with "Mailbox doesn't exist".
IMAP RENAME: If dest mailbox exists but source doesn't, fail with "Mailbox doesn't exist".

--HG--
branch : HEAD

jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,jkerihuel/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,jkerihuel/dovecot