debian/copyright: Fix the URL of the format spec

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
debian: Modernisation

Update to dh9 (with multi-arch paths disabled), standards-version 3.9.3,
and dh-autoreconf.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
gitignore: Ignore .dirstamp files too

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>