[schema] fix buggy composite_rdef_roles and associated test
it should only look at rdefs involving the considered entity type.
Closes #3712982
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))