Description:
------------
While the constructor of DateTime can handle negaive dates (BC dates), create_date_from_format cannot.

Reproduce code:
---------------
$d = new DateTime("-4000-01-31"); echo $d->format("Y-m-d"), PHP_EOL;
$d = date_create_from_format("Y-m-d", "4000-01-31"); echo $d->format("Y-m-d"), PHP_EOL;
$d = date_create_from_format("Y-m-d", "-4000-01-31"); echo $d->format("Y-m-d"), PHP_EOL;

Expected result:
----------------
-4000-01-31
4000-01-31
-4000-01-31

Actual result:
--------------
-4000-01-31
4000-01-31
PHP Fatal error:  Call to a member function format() on a non-object in Command line code on line 3