This patch contains the following changes to the SCSI tape driver:

- fixes EOM bug in large transfer in fixed block mode
- enables writing trailers by alternating error with ENOSPC and
  attempting a new write
- the write loop cleaned and simplified
- set the scatter/gather list element lengths to sum up to the
  desired transfer length
- MTERASE to use the short erase SCSI command if argument is zero
- set the can-bsr flag for drives with SCSI level >= 3
- C99 structure initializations
- some janitorial changes