Use dpkg-shlibdeps

This will change the build system to use the dpkg-shlibdeps command to generate dependencies from the actual build.

Currently I'm just leveraging the old pd-extended build scripts to do this. Unfortunately they use a really wonky shell-based hack to copy the output of dpkg-shlibdeps to the control file. But for now it seems to work.

Before merging we should test to make sure no dependencies have accidentally been dropped.