asyncFlow packaging should provide endowments, meta-operations

[erights]

See #9097

This does not affect the low level asyncFlow abstraction itself. But such conveniences must appear at the abstraction level immediately above it.

@mhofman , I'll leave this for you to describe, since you're already writing about this.

[erights]

For example, should add a meta operation for asking about the incarnation number of the next log state, that does not log the query, but would always give the same answer if asked at the same point. This would permit a successor to ask when its predecessor did not, and vice versa. (Suggested by @dtribble I think)