OK, I found a real solution: we can fix nodeWorktablescan.c so that the
order of initialization doesn't matter, by postponing the steps that
need information from the RecursiveUnion node until the first exec call
for the worktable node.
Although nodeCtescan is making a similar assumption about initialization
order, I think that one ought to be safe. We can always change it later
if need be.
regards, tom lane
