Change the source format from "1.0" to "3.0 (quilt)" because it works
more cleanly.

All files except .config and debian/ go into the orig tarball.
Add a single patch, debian/patches/config, and delete the ugly
extend-diff-ignore patterns.

The debian tarball will be compressed into *.debian.tar.xz by default.
If you like to use a different compression mode, you can pass the
command line option, DPKG_FLAGS=-Zgzip, for example.

The orig tarball only supports gzip for now. The combination of
gzip and xz is somewhat clumsy, but it is not a practical problem.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>