Fix SftpFileAttributes file type detection #1688
                
     Merged
            
            
          
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To get the file type, S_IFMT should be used as the mask. Instead it was using each file type as the mask. It meant that e.g. a symbolic link would also show as a regular file and a character device.
Also allow setting and retrieving the setuid/setgid/sticky bits
closes #1000
closes #159