Resolves #1731. Correctly handle nested alias that have hostnames. While here prevent putting duplicated dns hostnames under the same table to prevent possible hickups and save double work.
Related issues
Bug #1731: Hostnames are not allowed access when using an Alias in an Alias
Resolves #1731. Correctly handle nested alias that have hostnames. While here prevent putting duplicated dns hostnames under the same table to prevent possible hickups and save double work.