[schema] Make syntax compatible with print_function
yams seems to exec() us sometimes (instead of __import__()), and
yams.reader uses print_function nowadays.
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))