Description:
------------
The `pdo_mysql.default_socket` configuration setting is ignored when creating a 
PDO MySQL connection to "localhost"

On my system, `pdo_mysql.default_socket` is set to "/var/run/mysqld/mysqld.sock"

I've created a proof of concept here - http://staging.philipbrown.id.au/pdo-
test.php

Test script:
---------------
$db = new PDO('mysql:host=localhost;dbname=test', 'pdotest', 'pdotest');
echo $db->getAttribute(PDO::ATTR_SERVER_VERSION);


Expected result:
----------------
Expect to see MySQL server version, eg "5.1.37-1ubuntu5.5"

Actual result:
--------------
PDOException with message "SQLSTATE[HY000] [2002] Can't connect to local MySQL 
server through socket '/tmp/mysql.sock' (2)"