=item agentnum - Optional agentnum (see L<FS::agent>)
+=item title - an optional external string that identifies this
+referral source, such as an advertising campaign code.
+
=back
=head1 NOTE
|| $self->ut_text('referral')
|| $self->ut_enum('disabled', [ '', 'Y' ] )
#|| $self->ut_foreign_keyn('agentnum', 'agent', 'agentnum')
+ || $self->ut_textn('title')
|| ( $setup_hack
? $self->ut_foreign_keyn('agentnum', 'agent', 'agentnum' )
: $self->ut_agentnum_acl('agentnum', 'Edit global advertising sources')