update system.tar.inc to latest Archive_Tar (Pear)

upgrade to 1.4.0 stable
http://pear.php.net/package/Archive_Tar

1.4.0 stable
* Add support for PHP 7
* Drop support for PHP 4
* Add visibility declarations to methods and properties

Apart from the upgrades done to Tar.php at pear.net.net, there are known platform issues with the current versions for Drupal (system.tar.inc in Drupal 7 and ArchiveTar in Drupal 8):

1. On Windows, path names are translated wrongly and the result is that e.g. the backup and migrate module can generate backup files with wrong paths.
2. On Ubuntu 14.04 LTS (Trusty Tahr) 32 bit, gzopen() etc. are not defined. This results in White Screen Of Death (WSOD) for e.g. import/export configuration, install module and backup and migrate.