Re: automatically generating node support functions

I rebased this mostly out of curiousity.  I fixed some smallish
conflicts and fixed a typedef problem new in JSON support; however, even
with these fixes it doesn't compile, because JsonPathSpec uses a novel
typedef pattern that apparently will need bespoke handling in the
gen_nodes_support.pl script.  It seemed better to post this even without
that, though.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"El miedo atento y previsor es la madre de la seguridad" (E. Burke)