[web auth] fix authentication pb when anonymous are allowed, avoiding the first authentifier to return an anon connection while a following one may find correct authentication info. This make things simpler (eventually)

usr/lib/python2.4/site-packages/cubicweb/
etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/run/cubicweb
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances