sftp: Fix slow downloads for long latency connections - fixes #1158
sftp: Fix slow downloads for long latency connections - fixes #1158

This was caused by using the sftp.File.Read method which resets the
streaming window after each call.  Replacing it with sftp.File.WriteTo
and an io.Pipe fixes the problem bringing the speed to the same as the
sftp binary.

yonjah/rclone,ncw/rclone,B4dM4n/rclone,ncw/rclone,olihey/rclone,yonjah/rclone,B4dM4n/rclone,olihey/rclone,olihey/rclone,ncw/rclone,B4dM4n/rclone,B4dM4n/rclone,yonjah/rclone,yonjah/rclone,ncw/rclone,olihey/rclone