SFTP: Add truncate() to size() test for files larger than 4 GiB.
Merge pull request #490 from bantu/sftp-large-files

SFTP: Add truncate() to size() test for files larger than 4 GiB.

* bantu/sftp-large-files:
  SFTP: Add truncate() to size() test for files larger than 4 GiB.