> How we do what the spec wants isn't entirely clear, but maybe we could
> link all the supposed-to-track-each-other occurrences of NEXT VALUE FOR
> late in the planning stage or during executor startup, somewhat like
> what happens with aggregate functions.
Isn't there a statement level memory location that we could shove a
boolean variable? Then let the executor determine whether to call todays
version of nextval() or currval() based on that?
