OSDMap and OSDMap::Incremental instances with new osd uuid fields.
note forward_incompat changes from osd_peer_stat_t at
0.41-306-gfbbbd01
osd_peer_stat_t isn't in the old corpus, but it was contained by messages
that used it; mark those as forward_incompat (meaning new code won't
understand the old data).
We did this because it's an on-wire incompatibility only, and a new
feature bit protects us there.