Edited Issue: Path is not always resolved to fully qualified path in SftpClient [2543]

Just noticed that there are several methods in SftpClient (eg. OpenRead) that do not resolve the specified path to a fully qualified path before passing the path on to other part of SSH.NET.

This results a SftpPathNotFoundException (no such file) when you use ChangeDirectory to change the working directory, and subsequently specify a path relative to this directory.