Description:
------------
is_file method (probably all filestat method based) is not taking into account the php://filter shape when describing a file to open. This is pretty normal to write code like that:
if (is_file($path))
    throw new \Exception("File exists");

$file = open($path);
...

Unfortunately, is_file will always return false when a filter is used

Note: this issue is probably affecting ALL php versions

Test script:
---------------
ed@test:~$ php -v
PHP 5.6.29-0+deb8u1 (cli) (built: Dec 13 2016 16:02:08)
Copyright (c) 1997-2016 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies
    with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies
ed@test:~$ php -r 'var_dump(is_file("test"));'
bool(false)
ed@test:~$ php -r 'var_dump(is_file("php://filter/read=string.toupper/resource=test"));'
bool(false)
ed@test:~$ touch test
ed@test:~$ php -r 'var_dump(is_file("test"));'
bool(true)
ed@test:~$ php -r 'var_dump(is_file("php://filter/read=string.toupper/resource=test"));'
bool(false)