[wp-xmlrpc] WP 2.2.1 breaks Ruby 1.8.2

[Joe Cheng]

> My gut feeling is to support option 1, spelling out exactly what the
> format MUST be (yyyyMMddThh:mm:ssZ) for that field and that anything
> that does match that exactly is completely bogus.

If we do include the Z, then it needs to not use the XML-RPC date/time
datatype... which come to think of it, means people will have to parse
the date themselves. I think that's a good reason NOT to include the
Z.

And come to think of it, adding a timezone field instead of a GMT field
means people will have to parse a timezone, which no XML-RPC library
will help you with. Daniel, I think you were right--we should just do
dateCreatedUtc or whatever instead.