Small rewrite for better use of closeFile():

Small rewrite for better use of closeFile():
- closeFile() is now no longer be callable publicly. If a file needs to be
  closed, it can simply be set to NULL (or unset). Class fields which points to
  such objects (e.g. pointerInstance) should always be set to NULL and not
  removed as this may cause checks with is_null() to trigger an E_NOTICE:

<?php
error_reporting(E_ALL);

class Object {}

$var = new Object();

$isNull = is_null($var);
var_dump($isNull);

unset($var);

$isNull = is_null($var);
var_dump($isNull);
?>

  Being set to NULL or completly unset is a different thing.
- Updated 'core' to latest commit

Signed-off-by: Roland Haeder <roland@mxchange.org>