[CWEP002] properly handle serialization of computed relations
We now:
* have CWComputedRelation in the bootstrap schema to store computed relations
* properly serialize/deserialize it
* test first if the database has been migrated and contains the related table
Related to #3546717
[jcr: adjust unittest_querier to pass with the added entity type]
from datetime import datetime
for rtype in ('cw_support', 'cw_dont_cross', 'cw_may_cross'):
drop_relation_type(rtype)
add_entity_type('CWSourceSchemaConfig')
if not 'url' in schema['CWSource'].subjrels:
add_attribute('CWSource', 'url')
add_attribute('CWSource', 'parser')
add_attribute('CWSource', 'latest_retrieval')