Description:
------------
When loading connection information from a .cnf file, specified with PDO::MYSQL_ATTR_READ_DEFAULT_FILE, the hostname(s) defined in said file are apparently ignored and localhost is used instead.  Other information such as database, username, and password are indeed read and used...Just not the hostname.

Reproduce code:
---------------
<?php

/* This would be the contents of the "apps.cnf" file:
[client]
host=dbserve1

[app1]
database=app1
user=app1_user
password=shhhhh

[app2]
host=dbserve2
database=app2
user=app2_user
password=supersecret
*/

// try to connect using settings in .cnf file
$dbh = new PDO('mysql:', NULL, NULL, array(
    PDO::ATTR_TIMEOUT => 3,
    PDO::MYSQL_ATTR_READ_DEFAULT_FILE => '/var/mysql/apps.cnf',
    PDO::MYSQL_ATTR_READ_DEFAULT_GROUP => 'app1',
));

// tell us what happened
print_r($dbh->errorInfo());

?>

Expected result:
----------------
In lieu of any host/db/user information specified in the DSN, said info would be pulled from the .cnf file and the script would attempt to connect to the database 'app1' as 'app1_user' on host 'dbserve1'.

Actual result:
--------------
The script attempts to connect to the database 'app1' as 'app1_user' on host 'localhost'.