Simplify mkdatacd.sh

It is not necessary to create intermediate ISO anymore.  We pipe mkisofs
to cdrecord directly.
Restore -t option, "unpipe" mkisofs and cdrecord

We have problems when pipeing mkisofs and cdrecord (check commentaries
in the file), so create a intermediary iso.  Restore "-t" option to
specify temporary file for the iso image.
Drop group specification

We don't need it.  "name" is enough.
Add dar support
dar backup working
Update shx
Implement backup using tar
Divide dar and tar backups in its functions

And improve self documentation in commentaries.
Update shx