Restore compatibility with PHP 5.6.1 by using explicit array indexes.

This seems to be caused by the resolution of PHP Ticket 67985.
Merge pull request #493 from bantu/fix-491

Restore compatibility with PHP 5.6.1 by using explicit array index.

* bantu/fix-491:
  Restore compatibility with PHP 5.6.1 by using explicit array indexes.
SFTP: Add truncate() to size() test for files larger than 4 GiB.