[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)

"""pre 3.6 bw compat"""
# pylint: disable-msg=W0614,W0401
from warnings import warn
warn('moved to cubicweb.tags', DeprecationWarning, stacklevel=2)
from cubicweb.tags import *