TODO
====
- add support for capture_stderr option in constructor
- port to OpenVMS
- add support for later protocol versions
DONE
==== 
- add support for new extension methods available from late OpenSSH
  SFTP server (http://www.sfr-fresh.com/unix/misc/openssh-5.1.tar.gz:a/ssh/PROTOCOL)
- add support for unix2dos and dos2unix transformations on the fly for get and put .
- add support con restarting transfer to put, get and derived methods.