private static void
markAdditional(RRset rrset, Set names) {
	Record first = rrset.first();
	if (first.getAdditionalName() == null)
		return;

	Iterator it = rrset.rrs();
	while (it.hasNext()) {
		Record r = (Record) it.next();
		Name name = r.getAdditionalName();
		if (name != null)
			names.add(name);
	}
}
Looks up Records in the Cache (a wrapper around lookupRecords).  Unlike
lookupRecords, this given no indication of why failure occurred.
@param name The name to look up
@param type The type to look up
@return An array of RRsets, or null
@see Credibility
src/main/java/core/org/xbill/DNS/Cache.java