xbt_cfgelm_string, 1, 1, _sg_cfg_cb_context_factory, NULL);
xbt_cfg_setdefault_string(_sg_cfg_set, "contexts/factory", dflt_ctx_fact);
xbt_cfgelm_string, 1, 1, _sg_cfg_cb_context_factory, NULL);
xbt_cfg_setdefault_string(_sg_cfg_set, "contexts/factory", dflt_ctx_fact);