[datafeed parser] fix retrieve_url to always return urllib2.urlopen compatible output
as one should expect to be able to call geturl/getcode/info on the returned
object whatever the url he gave.
Related to #3682069
change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')