Fix CNAME chain handling when querying for a CNAME

[horkhe]

The repository looks abandoned but I decided to make this PR anyway.

• When CNAME is requested (e.g. LookupCNAME) only the top level CNAME record should be returned if existed. Previously server followed chain of CNAME records until a non-CNAME is reached and returned it. This is not how actual DNS server behaves. Note that behaviour to follow a CNAME chain when querying any other record is preserved, because that is how actual DNS server behaves.
• When there is chain of CNAMEs a request for any other record includes entire chain to the answer. Previously only one bogus CNAME record was included in the answer. from the original CNAME to the terminal non-CNAME record.
• SkipCNAMEs flag is ignored as no longer making any sense, but preserved in the code for backwards compatibility.