Update on Operating System detection in SFTP implementation has side effects on YADE

Current Situation
An update of the sos implementation of JCrafts SFTP to determine the remote operating system is not working correctly and has a side effect on YADE, The variable isUnix is not checked, instead the old variable isWindowsShell is checked but not set correctly beforehand.

Desired Behavior
The checking of a remote OS should not result in side effects for YADE. YADEs rename and move fuctionality has to work OS independently.