Use python3 shebang for scripts
Reported by lintian "python-script-but-no-python-dep"
for rtype in ('cw_support', 'cw_dont_cross', 'cw_may_cross'):
drop_relation_type(rtype)
if not 'url' in schema['CWSource'].subjrels:
add_attribute('CWSource', 'url')
add_attribute('CWSource', 'parser')
add_attribute('CWSource', 'latest_retrieval')