[optimization] traced_selection is used very intensively in debug mode
optimizing it is worth the pain. Basically : don't do stuff unnecessary
when we don't trace anything.
# pylint: disable-msg=W0614,W0401fromwarningsimportwarnwarn('moved to cubicweb.dataimport',DeprecationWarning,stacklevel=2)fromcubicweb.dataimportimport*