[dataimport] Drop reference to the 'source' column (closes #4067694).
CW 3.19 drops the multi-source support. This column does not exist in 3.19.
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))