https://github.com/PowerShell/Win32-OpenSSH/issues/479https://github.com/PowerShell/Win32-OpenSSH/issues/476https://github.com/PowerShell/Win32-OpenSSH/issues/474https://github.com/PowerShell/Win32-OpenSSH/issues/467
bug #479 - "ls c:" is not working
sanitized_path() is modified to handle the edge case "\x:"
2.bug #476 - "cd c:" is not working
If "c:" is passed to _fullpath() then it is returning existing path but not "c:", so if we append "\" to "c:" then it is working fine.
3.bug #474 - code cleanup MAX_PATH
Using PATH_MAX variable instead of MAX_PATH
In dirent.h, used PATH_MAX instead of hardcoding 256 characters
In readdir(), changed the pdirentry to be a static variable. Before this, we are leaking the memory.
4.bug #467 - SFTP rename failed if the newpath already exists.
The _wrename throws error if the newpath exists.
To make it consistent with the linux behavrior,
a) if the newpath is a file and if it exists then delete it so that _wrename will succeed.
b) if the newpath is a directory and if it is empty then delete it so that _wrename will succeed.
