[mdx] requesting all entities

[Tom Scavo]

As long as we're tweaking the spec, let me suggest we take another
look at section 3.2.2 (Request All Entities). I'll observe that there
is no normative language in that section.

First let me give a data point. The InCommon MDQ server will not serve
a full aggregate since that would compete with the aggregates
currently served from md.incommon.org.

That said, it's pretty obvious (to me) how that section might be
rewritten. Any given MDQ server MAY serve a full aggregate, but if it
does, it MUST do it like this...

Do we need to spell out that a "full aggregate" corresponds to the
totality of entities served individually, or is that obvious?

Tom