Description:
------------
When creating a pdo_mysql connection, database and hostname are required even when they are supplied in the my.cnf file.

Reproduce code:
---------------
contents of ~/.my.cnf:
[php]
user = myusername
password = mypassword
database = mydb
host = db.mydomain.com
default-character-set = utf8

PHP code to test usage of ~/.my.cnf:
<?
$pdo = new PDO('mysql:dbname=ppv',null,null,array(PDO::MYSQL_ATTR_READ_DEFAULT_GROUP=> 'php');

$st = $pdo->prepare("select user()");
$st->execute();
$rs = $st->fetchAll();
print_r($rs);
?>





Expected result:
----------------
myusername@db.mydomain.com

Actual result:
--------------
Fatal error: Uncaught exception 'PDOException' with message 'invalid data source name'

In the above example, "dbname" is still required even though a "database" was given in ~/.my.cnf.

The host given in ~/.my.cnf is also ignored, and PHP/mysql defaults to "localhost".

Interestingly enough, default_character_set is applied.