Compress puppet tarball more

- Use xz on Linux, bzip2 elsewhere (bzip2 is a bit better than gzip, and xz
is more than twice as good as bzip2).  tar can figure out what compression
has been used automatically
Merge branch 'master' into compress-puppet-more
Merge pull request #64 from InsolvencyService/compress-puppet-more

Compress puppet tarball more