debuild: Make it possible to install purr-data along with pd-l2ork.

This brings my debuild/Launchpad build stuff to the latest version which now allows pd-l2ork and purr-data to be installed on the same system. I already tested this, my latest builds can be found at https://launchpad.net/~dr-graef/+archive/ubuntu/pd-l2ork.xenial. Note that this only affects the debuild stuff, not any of the stuff in packages/linux_make/, so straight Debian package builds using tar_em_up.sh -B are not affected in any way.