Fix ALTER DEFAULT PRIVILEGES with duplicated objects

Specifying duplicated objects in this command would lead to unique
constraint violations in pg_default_acl or "tuple already updated by
self" errors.  Similarly to GRANT/REVOKE, increment the command ID after
each subcommand processing to allow this case to work transparently.

A regression test is added by tweaking one of the existing queries of
privileges.sql to stress this case.

Reported-by: Andrus
Author: Michael Paquier
Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/ae2a7dc1-9d71-8cba-3bb9-e4cb7eb1f44e@hot.ee
Backpatch-through: 9.5

src/backend/catalog/aclchk.c

@@ -1293,6 +1293,9 @@ SetDefaultACL(InternalDefaultACL *iacls)
 		ReleaseSysCache(tuple);
 
 	heap_close(rel, RowExclusiveLock);
+
+	/* prevent error when processing duplicate objects */
+	CommandCounterIncrement();
 }
 
 

src/test/regress/expected/privileges.out

@@ -1563,7 +1563,8 @@ SELECT has_table_privilege('regressuser1', 'testns.acltest1', 'INSERT'); -- no
  f
 (1 row)
 
-ALTER DEFAULT PRIVILEGES IN SCHEMA testns GRANT SELECT ON TABLES TO public;
+-- placeholder for test with duplicated schema and role names
+ALTER DEFAULT PRIVILEGES IN SCHEMA testns,testns GRANT SELECT ON TABLES TO public,public;
 SELECT has_table_privilege('regressuser1', 'testns.acltest1', 'SELECT'); -- no
  has_table_privilege 
 ---------------------

src/test/regress/sql/privileges.sql

@@ -933,7 +933,8 @@ CREATE TABLE testns.acltest1 (x int);
 SELECT has_table_privilege('regressuser1', 'testns.acltest1', 'SELECT'); -- no
 SELECT has_table_privilege('regressuser1', 'testns.acltest1', 'INSERT'); -- no
 
-ALTER DEFAULT PRIVILEGES IN SCHEMA testns GRANT SELECT ON TABLES TO public;
+-- placeholder for test with duplicated schema and role names
+ALTER DEFAULT PRIVILEGES IN SCHEMA testns,testns GRANT SELECT ON TABLES TO public,public;
 
 SELECT has_table_privilege('regressuser1', 'testns.acltest1', 'SELECT'); -- no
 SELECT has_table_privilege('regressuser1', 'testns.acltest1', 'INSERT'); -- no