Here is a new patch with the following changes on top of Heikki's
version (all the changes in which I've otherwise kept):
1. Changed TupleDescCopyEntry parameter order to be (dest,src) for
better consistency with TupleDescInitEntry and general C style.
2. Removed CreateTupleDescCopyExtend which is now dead code
3. Some small cleanups in the building of tupdescs in executor init
4. Refactored the grammar further to reinstant multi-arg unnest inside
table(), and added regression tests for that
5. comment and doc changes requested in Heikki's message
--
Andrew (irc:RhodiumToad)