[CWEP002] properly handle serialization of computed attributes Until this cset, only serialization of computed attribute's formula was handled (thanks to the relation definition's properties dict). We now: * properly serialize/deserialize attribute's formula * test first if the database has been migrated and contains related column or not Related to #3546717

from yams.buildobjs import RelationDefinition

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