When parsing messages use a hashtable instead of a linear search to
reduce the amount of work done in findname when there's more than one
name in the section.
There are two hashtables:
1) hashtable for owner names - that's constructed for each section when
we hit the second name in the section and destroyed right after parsing
that section;
2) per-name hashtable - for each name in the section, we construct a new
hashtable for that name if there are more than one rdataset for that
particular name.
(cherry picked from commit b8a9631754)
849c05adf4