Adds bztar format to generate .tar.bz2 tarballs

Uses the -f argument to overright old tarballs automatically, I am
assuming that if the old tarball was wanted it would have been moved or
else the version number would have been changed.

Uses the -9 argument to bzip2 and gzip to use maximum
compression. Compress uses the maximum compression by default.

Tests for correct value for the 'compress' argument of make_tarball. This
is one less place for someone adding new compression programs to forget to
change.