XML: upgrade-2.10.xsl: cluster options [3/3]: also allow redefining

See commit c1c66fe13.

Also make MapMsg (MapMsg-2) "function" and cibtr-2.rng accommodate
the new value modifier (@redefined-as) encoded in the upgrade "map".

Also further refine allowed cluster_property_set/nvpair/@name to
those beside the just-dropped (e.g. because of move) items as encoded
in the upgrade map.