Description:
------------
Since PostgreSQL 9.0, NOTIFY command accept a payload => http://www.postgresql.org/docs/9.0/static/sql-notify.html

The payload is available in the libpq's structure pgNotify.extra => http://www.postgresql.org/docs/9.0/static/libpq-notify.html

This field is available since PostgreSQL 7.4, but is empty until PostgreSQL 9.0 => http://www.postgresql.org/docs/7.4/static/libpq-notify.html

I provide a patch for PDO::pgsqlGetNotify() method which work for me. But I doubt which my check about libpq version is comply with the good practice.

Test script:
---------------
<?php
$dsn = 'pgsql:host=localhost;port=5432;dbname=postgres;user=admin;password=toto';
$db = new PDO($dsn);

$db->exec('LISTEN event;');
$db->exec('NOTIFY event, \'payload\';');
var_dump($db->pgsqlGetNotify());
?>

Expected result:
----------------
array(6) {
  [0]=>
  string(5) "event"
  [1]=>
  int(25876)
  [2]=>
  string(7) "payload"
  ["message"]=>
  string(5) "event"
  ["pid"]=>
  int(25876)
  ["payload"]=>
  string(7) "payload"
}


Actual result:
--------------
array(4) {
  [0]=>
  string(5) "event"
  [1]=>
  int(25876)
  ["message"]=>
  string(5) "event"
  ["pid"]=>
  int(25876)
}