[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
import ConfigParser
try:
undo_actions = config.cfgfile_parser.get('MAIN', 'undo-support', False)
except ConfigParser.NoOptionError:
pass # this conf. file was probably already migrated
else:
config.global_set_option('undo-enabled', bool(undo_actions))