Fix Binary on python < 2.7.4 (closes #10593811)
Before the fix for http://bugs.python.org/issue10211 we can't pass a
buffer object to BytesIO, so keep using StringIO in that case. And
because StringIO is an old-style class, we can't use super().
from yams.buildobjs import RelationDefinition
class ARelation(RelationDefinition):
subject = 'CWUser'
object = 'CWGroup'