merge unbound-1.13.2 / regen configure, ok florian

merge Unbound 1.9.6

Update to unbound-1.6.1rc3 - thanks millert@ and Brad for tests.

update to unbound-1.5.9. (there will be a follow-up commit to cherrypick a
couple of post-1.5.9 patches).

tests from Mark Patruck, danj, matthieu, millert. reads ok to jung, ok florian.