- if client certificates are not enabled, reset the saved alias value to
prevent them from being used anyway
- change enabling use of client certs for IMAP to an explicit checkbox
(like for SMTP) instead of implicitly based on use of auth type EXTERNAL
because some users may use ccerts with outher authentication types.
implementation is almost identical to the way it works for outgoing
server now, except for the extra logic that ccerts are _required_ when
auth type EXTERNAL is selected.