Portal and memory management infrastructure for extended query protocol.

Both plannable queries and utility commands are now always executed
within Portals, which have been revamped so that they can handle the
load (they used to be good only for single SELECT queries).  Restructure
code to push command-completion-tag selection logic out of postgres.c,
so that it won't have to be duplicated between simple and extended queries.
initdb forced due to addition of a field to Query nodes.

src/include/nodes/parsenodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: parsenodes.h,v 1.236 2003/03/27 16:51:29 momjian Exp $
+ * $Id: parsenodes.h,v 1.237 2003/05/02 20:54:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -47,6 +47,8 @@ typedef struct Query
 
 	QuerySource	querySource;	/* where did I come from? */
 
+	bool		canSetTag;		/* do I set the command result tag? */
+
 	Node	   *utilityStmt;	/* non-null if this is a non-optimizable
 								 * statement */