Deformed spline should be re-evaluated after adding new feather points Used both BKE_mask_update_display and DAG_id_tag_update because of: - If adding feather point is happening from macro which adds point and slides it, deformed spline should be updated immediatelly so sliding operator will use updated feather, - If adding happens outside of such macro, update DAG is necessary to make needed updates in other areas (such as compositor, i.e.)