plpythonu DO support (inline call handler)

Hi,

The attached patch adds support for DO clause in plpythonu. It was
heavily inspired by the plperl and plpgsql inline handler code.

I couldn't figure out how to get added files to show in git diff so the
two files that this patch adds: expected/plpython_do.out and
expected/plpython_do.sql are added as diff -uN 's in plpython_do_sql.diff

- Hannu

ps.
(This is a resend of the patch since I sent it a couple of days ago and
the original message seems to have been lost to the moderation queue so
now I subscribed.)