allow 1-char domain names

interface/lib/classes/remote.d/dns.inc.php

interface/web/admin/form/server_config.tform.php

interface/web/client/form/domain.tform.php

interface/web/dns/dns_wizard.php

interface/web/dns/form/dns_slave.tform.php

interface/web/dns/form/dns_soa.tform.php

interface/web/mail/ajax_get_json.php

interface/web/mail/form/mail_aliasdomain.tform.php

interface/web/mail/form/mail_domain_catchall.tform.php

interface/web/mail/form/mail_mailinglist.tform.php

interface/web/mail/form/xmpp_domain.tform.php