Re: Oversight in reparameterize_path_by_child leading to executor crash

I looked over the v3 patch.  I think it's going in generally
the right direction, but there is a huge oversight:
path_is_reparameterizable_by_child does not come close to modeling
the success/failure conditions of reparameterize_path_by_child.
In all the cases where reparameterize_path_by_child can recurse,
path_is_reparameterizable_by_child has to do so also, to check
whether the child path is reparameterizable.  (I'm somewhat
disturbed that apparently we have no test cases that caught that
oversight; can we add one cheaply?)

BTW, I also note from the cfbot that 9e9931d2b broke this patch by
adding more ADJUST_CHILD_ATTRS calls that need to be modified.
I wonder if we could get away with having that macro cast to "void *"
to avoid needing to change all its call sites.  I'm not sure whether
pickier compilers might warn about doing it that way.

            regards, tom lane