* limiting domain names to 255/63 octets/labels (#463)
(cherry picked from commit 0b729df06c)
* account for \ and \xxx in presentation format
(cherry picked from commit a094f774892fb4305051d185c2488cb43200c4d9)
* go fmt
* Add tests for UnpackDomainName
Domain names must not exceed 255 octets in wire format.
Ref gh-463
Ref gh-469
* Fix UnpackDomainName
* Introduce a long-domain sentinel error
A typed error would be better, but inconsistent with this library.
cf. https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully
Richard Gibson