data.tar.xz support added to Launchpad

[Colin Watson]

It should now be possible to use xz compression for .deb packages
uploaded to Ubuntu oneiric (using 'dh_builddeb -- -Zxz').  In order to
do so, you must include this field in the relevant binary packages:

  Pre-Depends: dpkg (>= 1.15.6)

(This implies that such packages can only be uploaded to maverick and
later.)

Please do not use this for packages that are Priority: required or
Priority: important, as you will break the installer if you do (and
relaxing that restriction would have implications for people's ability
to debootstrap Ubuntu on various minimal systems).

Please check that it's actually worth compressing a package using xz
before doing so!  You can easily take the data.tar.gz, recompress it
using xz, and compare the size.

If you maintain a package that already uses -Zlzma, consider converting
it to -Zxz; compression ratios should be similar, and it's a
better-designed format.

-- 
Colin Watson                                       [cjwatson at ubuntu.com]