Make RLS related error messages more consistent and compliant.

Also updated regression expected output to match. Noted and patch by Daniele Varrazzo.

src/backend/commands/policy.c

@@ -563,7 +563,7 @@ CreatePolicy(CreatePolicyStmt *stmt)
 	if (HeapTupleIsValid(policy_tuple))
 		ereport(ERROR,
 				(errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("policy \"%s\" for relation \"%s\" already exists",
+				 errmsg("policy \"%s\" for table \"%s\" already exists",
 				 stmt->policy_name, RelationGetRelationName(target_table))));
 
 	values[Anum_pg_policy_polrelid - 1] = ObjectIdGetDatum(table_id);
@@ -735,7 +735,7 @@ AlterPolicy(AlterPolicyStmt *stmt)
 	if (!HeapTupleIsValid(policy_tuple))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
-				 errmsg("policy \"%s\" on table \"%s\" does not exist",
+				 errmsg("policy \"%s\" for table \"%s\" does not exist",
 						stmt->policy_name,
 						RelationGetRelationName(target_table))));
 
@@ -977,7 +977,7 @@ get_relation_policy_oid(Oid relid, const char *policy_name, bool missing_ok)
 		if (!missing_ok)
 			ereport(ERROR,
 					(errcode(ERRCODE_UNDEFINED_OBJECT),
-					 errmsg("policy \"%s\" for table  \"%s\" does not exist",
+					 errmsg("policy \"%s\" for table \"%s\" does not exist",
 							policy_name, get_rel_name(relid))));
 
 		policy_oid = InvalidOid;

src/backend/commands/user.c

@@ -301,7 +301,7 @@ CreateRole(CreateRoleStmt *stmt)
 		if (!superuser())
 			ereport(ERROR,
 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-				errmsg("must be superuser to change bypassrls attribute.")));
+				errmsg("must be superuser to change bypassrls attribute")));
 	}
 	else
 	{

src/test/regress/expected/rowsecurity.out

@@ -1988,7 +1988,7 @@ GRANT ALL ON y1, y2 TO rls_regress_user1;
 CREATE POLICY p1 ON y1 FOR ALL USING (a % 2 = 0);
 CREATE POLICY p2 ON y1 FOR SELECT USING (a > 2);
 CREATE POLICY p1 ON y1 FOR SELECT USING (a % 2 = 1);  --fail
-ERROR:  policy "p1" for relation "y1" already exists
+ERROR:  policy "p1" for table "y1" already exists
 CREATE POLICY p1 ON y2 FOR ALL USING (a % 2 = 0);  --OK
 ALTER TABLE y1 ENABLE ROW LEVEL SECURITY;
 ALTER TABLE y2 ENABLE ROW LEVEL SECURITY;