kes Make DEVICE fd private. Its new name is m_fd, and can be

     obtained with dev->fd() outside the class.  This is the
     first of many DEVICE members to be made private.
kes  Implement Michael Renner's idea on having a virtual disk
     changer. I made some minor modifications (e.g. I did not
     implement the Virtual Changer directive, but simply set
     the Changer Command to an empty string.