improving the error message for executeEmulateQuery

Hello, handing a invalid statement to $db->execute() raised an error with the last SQL statement as debuginfo. It cost stupid me quite some time, because I started looking for the mistake around that SQL statement. I didn't find the location in the code where the last_query is used as debuginfo, but I think it would be a good idea to have a message like "invalid statement identifier" or something similiar instead. This works for me (in common.php, executeEmulateQuery()): if (!isset($this->prepare_tokens[$stmt]) ||

           !is_array($this->prepare_tokens[$stmt]) ||
           !sizeof($this->prepare_tokens[$stmt]))
       {
           return $this->raiseError(DB_ERROR_INVALID, null, null, 'invalid statement identifier');
       }

Vinai