Addition of more wildcarding

Wanted to note a proposed addition to core that I made for this draft, since
it hadn't been discussed formally. It was a small addition, so I can yank it
out easily, no big deal, but I think we should permit <anyAttribute> in the
root types (AssertionType, RequestAbstractType, StatusResponseType). Just
good practice to build in some wiggle room at the key spots, I think.

All wildcarding in the schemas is enforced in prose such that all extensions
must be namespace qualified (global), so there's no collision danger.

We can formally vote yea/nay next call.

-- Scott