Implement DROP OWNED and REASSIGN OWNED. These new commands facilitate the

process of dropping roles by dropping objects owned by them and privileges
granted to them, or giving the owned objects to someone else, through the
use of the data stored in the new pg_shdepend catalog.

Some refactoring of the GRANT/REVOKE code was needed, as well as ALTER OWNER
code.  Further cleanup of code duplication in the GRANT code seems necessary.

Implemented by me after an idea from Tom Lane, who also provided various kind
of implementation advice.

Regression tests pass.  Some tests for the new functionality are also added,
as well as rudimentary documentation.

src/include/commands/tablecmds.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/commands/tablecmds.h,v 1.24 2005/10/15 02:49:44 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/commands/tablecmds.h,v 1.25 2005/11/21 12:49:32 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -24,6 +24,8 @@ extern void RemoveRelation(const RangeVar *relation, DropBehavior behavior);
 
 extern void AlterTable(AlterTableStmt *stmt);
 
+extern void ATExecChangeOwner(Oid relationOid, Oid newOwnerId, bool recursing);
+
 extern void AlterTableInternal(Oid relid, List *cmds, bool recurse);
 
 extern void AlterTableCreateToastTable(Oid relOid, bool silent);