Description:
------------
Phar::extractTo() does not allow specific directories to be extracted. The 
documentation states the second parameter can be a file or directory to only 
extract the file or directory from the phar archive.

Specific files can be extracted however an exception is thrown when a directory is 
passed.

Test script:
---------------
<?php
  $phar = new Phar('/tmp/test.phar');
  $phar->buildFromDirectory('/path/to/source');
  unset($phar);

  $phar = new Phar('/tmp/test.phar');
  $phar->extractTo('/tmp/test/', 'subdir1/subdir2/', true); // throws exception
//  $phar->extractTo('/tmp/test/', 'subdir1/subdir2/file.txt', true); // works as intended
?>


Expected result:
----------------
The specific directory should be extracted from the phar archive.

Actual result:
--------------
Fatal error: Uncaught exception 'PharException' with message 'Phar Error: 
attempted to extract non-existent file "subdir1/subdir2/" from phar 
"/tmp/test.phar"' in /phar-test.php on line 7