[py3k] introduce cubicweb._ (related to #7589459) The end goal is to stop relying on '_' being in the builtin scope. In the mean time, deprecate the builtin '_' so that consumers are warned.

from yams.buildobjs import RelationDefinition

class ARelation(RelationDefinition):
    subject = 'CWUser'
    object = 'CWGroup'