SplitDomainName would always include the '.' after each label segment. This was
inconsistent with the "." case (were it returned nil) and didn't seem too useful
since it required more processing to remove the '.' (like when building a
compression dictionary in Msg.Len() or Msg.Pack()). It also had issues with the
last segment, not including it in the split. It now returns all segments,
including the last, irrespective of the label being fully qualified.
A test has also been added to ensure no regressions.
