Description:
------------
When using the DateTime class, it would make more sense to have getLastErrors be 
an instance method rather than a static method. That way, when creating a series 
of DateTime objects, you can check each one individually for errors.

Currently it works as _documented_, but not in a very logical/useful way.

Alternately, a getErrors() instance method that could sit alongside the 
getLastErrors() static method would be just as useful.

Test script:
---------------
<?php
date_default_timezone_set('America/Los_Angeles');
$a = array(
	DateTime::createFromFormat('Y m d', '2009 01 31'),
	DateTime::createFromFormat('Y m d', '2009 02 28'),
	DateTime::createFromFormat('Y m d', '2009 02 29'), // 2009 not leap year
	DateTime::createFromFormat('Y m d', '2008 02 29'), // 2008 is leap year
);
foreach ($a as $b) {
	print_r($b->getLastErrors());
}

Expected result:
----------------
Array
(
    [warning_count] => 0
    [warnings] => Array
        (
        )

    [error_count] => 0
    [errors] => Array
        (
        )

)
Array
(
    [warning_count] => 0
    [warnings] => Array
        (
        )

    [error_count] => 0
    [errors] => Array
        (
        )

)
Array
(
    [warning_count] => 1
    [warnings] => Array
        (
            [10] => The parsed date was invalid
        )

    [error_count] => 0
    [errors] => Array
        (
        )

)
Array
(
    [warning_count] => 0
    [warnings] => Array
        (
        )

    [error_count] => 0
    [errors] => Array
        (
        )

)

Actual result:
--------------
Array
(
    [warning_count] => 0
    [warnings] => Array
        (
        )

    [error_count] => 0
    [errors] => Array
        (
        )

)
Array
(
    [warning_count] => 0
    [warnings] => Array
        (
        )

    [error_count] => 0
    [errors] => Array
        (
        )

)
Array
(
    [warning_count] => 0
    [warnings] => Array
        (
        )

    [error_count] => 0
    [errors] => Array
        (
        )

)
Array
(
    [warning_count] => 0
    [warnings] => Array
        (
        )

    [error_count] => 0
    [errors] => Array
        (
        )

)