[idn] change to requirements

["Eric A. Hall" <ehall@ehsco.com>]

I suppose that it wasn't seen necessary to mandate the obvious, but we
need to add the following to section 2.1 of the requirements document:

 [n] The service MUST ensure that all of the authoritative servers
     for a zone will answer an identical query with identical answers.

-- 
Eric A. Hall                                        http://www.ehsco.com/
Internet Core Protocols          http://www.oreilly.com/catalog/coreprot/