required timezone xsd dateTime datatype (ISSUE-138)

Discussion in the XML Schema WG on 29 September 2008 chronicled at
http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2008Sep/0025.html
indicates that they will indeed have a datatype that is xsd:dateTime
with a required timezone.  They will also have a facet for xsd:dateTime
that indicates whether the timezone is required, forbidden, or optional.

The net result is that we can eventually use an xsd name for
owl:dateTime.  However, I suggest that this does not need to be
reflected in the current round of publication. 

peter