closest encloser from yy for DS zz. while building chain of trust,
because of a bug in the TTL-fix in 1.4.15, it picked the wrong rdata
for an NSEC3. Now it does not change rdata, and fixes TTL.
git-svn-id: file:///svn/unbound/trunk@2599 be551aaa-1e26-0410-a405-d3ace91eadb9