CDB_ColumnNames uses schema and table name from regclass

Fixes #122

scripts-available/CDB_ColumnNames.sql

@@ -3,11 +3,12 @@ CREATE OR REPLACE FUNCTION CDB_ColumnNames(REGCLASS)
 RETURNS SETOF information_schema.sql_identifier
 AS $$
 
-    SELECT column_name 
-      FROM information_schema.columns 
-      WHERE
-        table_name IN (SELECT CDB_UserTables())
-        AND table_name = '' || $1 || '';
+    SELECT c.column_name
+      FROM information_schema.columns c, pg_class _tn, pg_namespace _sn
+      WHERE table_name = _tn.relname
+        AND table_schema = _sn.nspname
+        AND _tn.oid = $1::regclass::oid
+        AND _sn.oid = _tn.relnamespace;
          
 $$ LANGUAGE SQL;