[selectors] fix is_instance bug w/ parent classes. Also slight performance enhancements by changing what's returned by vreg['etypes'].parent_classes method (dedicated for this usage...) and removing no more necessary methods
add_relation_type('prefered_form')
rql('SET X prefered_form Y WHERE Y canonical TRUE, X identical_to Y')
commit()
drop_attribute('EmailAddress', 'canonical')
drop_relation_definition('EmailAddress', 'identical_to', 'EmailAddress')
if 'see_also' in schema:
sync_schema_props_perms('see_also', syncprops=False, syncrdefs=False)