[security-services] Are the "use" attributes in the schema correct?

If I'm not mistaken, I think the XML attribute definitions in the
schemas need to be double checked against the intent of the
specification.

For example, I think it's intended that the Name and SecurityDomain
attributes in the NameIdentifier be required, but you can currently omit
both and still validate. There are some other examples where the core
doc says something is required in the text, but the use attribute is
missing.

I just double checked that the default value of the "use" option for
<attributes> in XML schema is "optional". From what I can tell, it may
be that the schema is written with the opposite assumption.

-- Scott