regenerate pristine tarballs

 pristine-tar can regenerate a pristine upstream tarball using only a small
 binary delta file and a revision control checkout of the upstream branch.
 .
 The package also includes a pristine-gz command, which can regenerate a
 pristine .gz file, a pristine-bz2 for .bz2 files, and a pristine-xz for .xz
 files.
 .
 The delta file is designed to be checked into revision control along-side
 the upstream branch, thus allowing Debian packages to be built entirely
 using sources in revision control, without the need to keep copies of
 upstream tarballs.