[login] fix the redirect url after login (closes #11689118) redirecting to '/' by default after login doesn't work properly when a prefix is used, whether we're sitting behind a PrefixMiddleware or not. To fix this, rely on cubicweb's build_url to turn any relative path into an absolute url.

include *.txt *.ini *.cfg *.rst
recursive-include sampleapp *.ico *.png *.css *.gif *.jpg *.pt *.txt *.mak *.mako *.js *.html *.xml