PostgreSQL FDW update

I needed something to test the FDW API patch with, and didn't want to 
get involved in the COPY API changes, and also wanted to have something 
that needs real connection management and can push down quals. So I 
updated the postgresql_fdw patch to work with the latest FDW patch.

Here. It's a bit of a mess, but it works for simple queries..

It requires a small change to the FDW api 
(fdw-api-add-serverid-userid.patch). I added server oid and user oid 
fields to the FdwPlan - that seems like basic information that most 
FDW's will need, so it seems awkward to require the FDW to wrap them in 
Const nodes and a List.

These are also available in my git repository at 
git://git.postgresql.org/git/users/heikki/postgres.git, branches fdw2 
and postgresql_fdw.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com