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/include/commands/cluster.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/commands/cluster.h,v 1.39 2010/02/04 00:09:14 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/commands/cluster.h,v 1.40 2010/02/07 20:48:13 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -25,9 +25,9 @@ extern void check_index_is_clusterable(Relation OldHeap, Oid indexOid,
 extern void mark_index_clustered(Relation rel, Oid indexOid);
 
 extern Oid	make_new_heap(Oid OIDOldHeap, Oid NewTableSpace);
-extern void swap_relation_files(Oid r1, Oid r2, bool swap_toast_by_content,
-					TransactionId frozenXid);
-extern void cleanup_heap_swap(Oid OIDOldHeap, Oid OIDNewHeap,
-							  bool swap_toast_by_content);
+extern void finish_heap_swap(Oid OIDOldHeap, Oid OIDNewHeap,
+							 bool is_system_catalog,
+							 bool swap_toast_by_content,
+							 TransactionId frozenXid);
 
 #endif   /* CLUSTER_H */