Description:
------------
::compress modifies archive basename.

Test script:
---------------
<?php
$files = ['a.txt'];

$arch = new \PharData('foo-1.2.3.tar');
foreach ($files as $file) {
	$arch->addFile($file);
}
$arch->compress(\Phar::GZ);


Expected result:
----------------
foo-1.2.3.tar.gz

Actual result:
--------------
foo-1.tar.gz