add support for CAS2 alongside WIND

Please note that since our test service is not returning affiliations,
the affiliations/group parsing/handling part is speculative, with
a unit test based on the official CAS specs. So *ought* to be right
but hasn't actually been tested against Columbia's CAS service.
s/cas/cas2/ in preparation for adding SAML alongside
add CAS3 + SAML 1.1 support
version bump
strip out prints
better handling of admin login

django admin overrides the normal login mechanism, not giving our view a chance
to stick the final destination URL in the session. CAS requires that
when we validate the ticket, we also send along that final destination URL
that we originally specified.

So, in our caslogin view, if we don't see a cached URL in the session,
we take our best guess and assume that it was the admin login that
got us into this situation and try to generate the equivalent URL
that would match that scenario.
Merge pull request #3 from ccnmtl/cas

add support for CAS2 alongside WIND