[web/debug] Fix check for open sessions
itervalues returns an iterator, which never evaluates to False.
Regression from 0bb18407c053 "[toward py3k] rewrite dict.keys() and
dict.values() (part of #2711624)".
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')