cubicweb #2465877 loggout regression on sites where anonymous are allowed [open]

we used to see a nice message "you've been deconnected". Now we get "you're not allowed to access this view" or alike.

NB: I also suspect a pb when one try to log, mistype login/pwd, get back to the login form but with "postlogin_path" linking to the very same form. Then you get similar "no access to view" message when login succeed

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