Fix run-time zone addition for secure zones.

https://fedorahosted.org/bind-dyndb-ldap/ticket/56
Fix run-time zone addition for invalid secure zones.

It is important *not* to delete invalid zones to prevent
ldap_parse_master_zoneentry() from entering infinite cycle.

Zone addition in ldap_parse_master_zoneentry() enforces serial
write-back to LDAP. This write generates LDAP modify event which
again triggers ldap_parse_master_zoneentry() and so on.

https://fedorahosted.org/bind-dyndb-ldap/ticket/56
Add wrappers for isc_task_*exclusive().

Signed-off-by: Petr Spacek <pspacek@redhat.com>
Delete old database & journal files during zone loading.

This prevents inline-signed zones from failing to receive updates from
LDAP mysteriously.

https://fedorahosted.org/bind-dyndb-ldap/ticket/56

Signed-off-by: Petr Spacek <pspacek@redhat.com>
Support run-time changes in idnsSecInlineSigning attribute.

https://fedorahosted.org/bind-dyndb-ldap/ticket/56

Signed-off-by: Petr Spacek <pspacek@redhat.com>