sftp server submodule for OpenSSH

 Green End SFTP Server is an SFTP server
 supporting up to protocol version 6.
 It is possible to use it
 as a drop-in replacement for the OpenSSH server
 (which supports only protocol version 3).
 .
  * Protocol versions 3 and higher:
    * Upload and download files
    * List files
    * Create directories and symbolic links
    * Rename and delete files
  * Protocol versions 4 and higher:
    * Filename encoding translation
    * Text mode transfers
    * String owner/group names (instead of numeric)
    * Sub-second timestamps (where supported by server OS)
  * Protocol versions 5 and higher:
    * Extended rename semantics (e.g. atomic overwrite)
  * Protocol versions 6 and higher:
    * Create hard links
  * Several SFTP extensions
 .
 Features of SFTP protocol versions are listed more detailed
 at <http://www.greenend.org.uk/rjk/sftp/sftpversions.html>.
 .
 Features beyond the v3 set depend on suitable client support.
 A list of clients and the versions they support
 is at <http://www.greenend.org.uk/rjk/sftp/sftpimpls.html>.