Create a "relation mapping" infrastructure to support changing the relfilenodes

of shared or nailed system catalogs.  This has two key benefits:

* The new CLUSTER-based VACUUM FULL can be applied safely to all catalogs.

* We no longer have to use an unsafe reindex-in-place approach for reindexing
  shared catalogs.

CLUSTER on nailed catalogs now works too, although I left it disabled on
shared catalogs because the resulting pg_index.indisclustered update would
only be visible in one database.

Since reindexing shared system catalogs is now fully transactional and
crash-safe, the former special cases in REINDEX behavior have been removed;
shared catalogs are treated the same as non-shared.

This commit does not do anything about the recently-discussed problem of
deadlocks between VACUUM FULL/CLUSTER on a system catalog and other
concurrent queries; will address that in a separate patch.  As a stopgap,
parallel_schedule has been tweaked to run vacuum.sql by itself, to avoid
such failures during the regression tests.

src/bin/pg_dump/pg_dump.c

@@ -12,7 +12,7 @@
  *	by PostgreSQL
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/bin/pg_dump/pg_dump.c,v 1.569 2010/01/28 23:21:12 petere Exp $
+ *	  $PostgreSQL: pgsql/src/bin/pg_dump/pg_dump.c,v 1.570 2010/02/07 20:48:10 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2300,6 +2300,12 @@ binary_upgrade_set_relfilenodes(PQExpBuffer upgrade_buffer, Oid pg_class_oid,
 	Oid			pg_class_reltoastrelid;
 	Oid			pg_class_reltoastidxid;
 
+	/*
+	 * Note: we don't need to use pg_relation_filenode() here because this
+	 * function is not intended to be used against system catalogs.
+	 * Otherwise we'd have to worry about which versions pg_relation_filenode
+	 * is available in.
+	 */
 	appendPQExpBuffer(upgrade_query,
 					  "SELECT c.relfilenode, c.reltoastrelid, t.reltoastidxid "
 					  "FROM pg_catalog.pg_class c LEFT JOIN "