patch: inline code with params

Hello

I updated my two years old patch
http://archives.postgresql.org/pgsql-hackers/2010-07/txtIakTCBA15Z.txt

Syntax is based on Florian Pflog's proposal
http://archives.postgresql.org/pgsql-hackers/2010-07/msg00110.php

postgres=# do (a int, b int, text) $$begin raise notice '% % %', $1,
$2, $3; end; $$ language plpgsql using 10+100,20, :'USER';
NOTICE:  110 20 pavel
DO

This patch is not final - missing documentation, regress tests, and
doesn't support subselects as expr.