- Modify open() for tape so nonblocking really works.

- Use fcntl() to reset blocking status rather than close()
  and reopen the drive.
- Make sure dev->open() is always called so that any change
  in read/write permissions will occur.
- Open drives initially in daemon in read-only mode.
- Ensure that each time the VolHdr.VolumeName is zapped
  or changed that free_volume() is called on the old name.