Yes, really, the ackno can appear to go backwards.

Think reordering. I'm surprised that it goes backwards otherwise,
but what can one do?
Improve primary new-view-change by reordering code.
Correct simultaneous attempt to enter a new view.

Before, we could have two partitions trying to enter a new view
at the same time, with the same new view number. (Reason: join.)
(*) Make one of them win, based on a total ordering of views.
(*) Don't adopt new views until they are confirmed.