Return proper 401/403 when access denied

Fixes #584

test/fixtures/privileges.sql

@@ -17,6 +17,7 @@ GRANT ALL ON TABLE
     , comments
     , complex_items
     , compound_pk
+    , empty_table
     , has_count_column
     , has_fk
     , insertable_view_with_join

test/fixtures/schema.sql

@@ -458,6 +458,13 @@ CREATE TABLE empty_table (
 );
 
 
+--
+-- Name: private_table; Type: TABLE; Schema: test; Owner: -
+--
+
+CREATE TABLE private_table ();
+
+
 --
 -- Name: has_count_column; Type: VIEW; Schema: test; Owner: -
 --