...thanks to using SocialLogin.stash/unstash_state.
Also:
- Some tests are updated to get the stash_state. Requests are denied if
client session doesn't go through stash_state (called in LoginCASView).
- Fix an assert statement in a test.
Renew paramater:
- By default, CAS client will use renew parameter if user already
authenticates via a CAS server. If always False, he can't
reauthenticate on a CAS server due to the single sign-on CAS feature
(except if he logouts of CAS on his own).
Tests:
- patch_cas_reponse now returns a correct CAS client taking into
account the version attribute of the CAS adapter.
- Some moves happens between testcases et al.
- Delete old and now unused fake CAS client classes.
