Identity switch behavior

[Cantor, Scott]

About all that's left to code regarding authentication is what to do on an
identity switch (the thing that causes so many problems right now in V2).

While I'm willing to build in some extensibility, above and beyond the
basic ability with SWF to make it do really anything somebody wants, I'm
not sure there's anything rational to do in general but purge the existing
session and replace it with a new one.

I could error out I suppose, but that seems pointless.

At some future point, I *could* build in some kind of logout operation
that would notify SPs in the original session, but absent having that code
in place I don't have any ideas beyond the above.

(I also think that such a logout would have to be fairly invisible and
avoid any obvious feedback to the user, since doing so would all but
scream "go here to steal some guy's data".)

-- Scott