Synchronize error messages.

Commits 6476b261
and 14f67a8e didn't use quite the
same error message for what is basically the same situation.

Amit Langote, pared back a bit by me.

Discussion: http://postgr.es/m/54dc76d0-3b5b-ba5a-27dc-fb31a3975b61@lab.ntt.co.jp

src/backend/catalog/partition.c

@@ -988,7 +988,7 @@ check_default_allows_bound(Relation parent, Relation default_rel,
 	if (PartConstraintImpliedByRelConstraint(default_rel, def_part_constraints))
 	{
 		ereport(INFO,
-				(errmsg("partition constraint for table \"%s\" is implied by existing constraints",
+				(errmsg("updated partition constraint for default partition \"%s\" is implied by existing constraints",
 						RelationGetRelationName(default_rel))));
 		return;
 	}
@@ -1033,7 +1033,7 @@ check_default_allows_bound(Relation parent, Relation default_rel,
 													 def_part_constraints))
 			{
 				ereport(INFO,
-						(errmsg("partition constraint for table \"%s\" is implied by existing constraints",
+						(errmsg("updated partition constraint for default partition \"%s\" is implied by existing constraints",
 								RelationGetRelationName(part_rel))));
 
 				heap_close(part_rel, NoLock);

src/test/regress/expected/alter_table.out

@@ -3345,7 +3345,7 @@ INFO:  partition constraint for table "part_3_4" is implied by existing constrai
 -- check if default partition scan skipped
 ALTER TABLE list_parted2_def ADD CONSTRAINT check_a CHECK (a IN (5, 6));
 CREATE TABLE part_55_66 PARTITION OF list_parted2 FOR VALUES IN (55, 66);
-INFO:  partition constraint for table "list_parted2_def" is implied by existing constraints
+INFO:  updated partition constraint for default partition "list_parted2_def" is implied by existing constraints
 -- check validation when attaching range partitions
 CREATE TABLE range_parted (
 	a int,
@@ -3492,7 +3492,7 @@ DROP TABLE quuux1, quuux2;
 -- should validate for quuux1, but not for quuux2
 CREATE TABLE quuux1 PARTITION OF quuux FOR VALUES IN (1);
 CREATE TABLE quuux2 PARTITION OF quuux FOR VALUES IN (2);
-INFO:  partition constraint for table "quuux_default1" is implied by existing constraints
+INFO:  updated partition constraint for default partition "quuux_default1" is implied by existing constraints
 DROP TABLE quuux;
 --
 -- DETACH PARTITION