Some login flow redesign

[Cantor, Scott]

After Daniel checked in the LDAP flow, I did some rethinking about how to
handle basic-auth along with form login, and I think I can merge these in
a reasonable fashion that should simplify having both options and make it
one webflow for any back-end doing either basic or form.

The testbed will undergo some login flow changes as a result, once I
verify that the idea works.

We're also in flux redoing a bit of the event handling for detecting
conditions like expiring passwords, so it will be changing a little in
that respect also.

-- Scott