[packagekit] xz tarballs

[Richard Hughes]

I've just committed a patch to PackageKit to enable xz tarballs. This
means we won't now generate .tar.gz and .tar.bz2 tarballs of the
release anymore. This has been done to reduce the amount of storage we
require for each release, and to bring us into the current decade
using a modern and fast compression format.

The only distros that can't support xz are ancient versions of
Solaris, which I don't care too much about. If this change is
problematic for you, yell, and I can always turn on .tar.bz2 again if
we really need it.

Thanks,

Richard.