Move to dh-9

Axel Beckert suggested this move to easily incorporate
dpkg-buildflags settings into the package's build process.

As a result, lintian now shuts up about missing hardening flags.

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Remove duplicate build trigger from build-stamp target

I can't remember why I put it in in the first place and it seems to
work fine without this step. So let's get rid of it. I can always
revert the change if something breaks.

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Update debian/changelog

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>