A common recovery is sometimes suffered with double voucher, which occurs when the person first vouched to warranty, comes in and vouches over a third person. 2. The necessity for double voucher arises when the tenant in tail is not the tenant in the writ, but is tenant by warranty; that is, where he is vouched, and comes in and confesses the warranty. Generally speaking, to accomplish this result, a previous conveyance is necessary, by the tenant in tail, to a third person, in order to make such third person tenant to a writ of entry.