Use git-packagebuild to handle the builds

[pazdera]

There is a tool that supports package builds from git (just as dr does), called git-pacakgebuild. It could be easier to work with instead of building in a foreign chroot.

Suggested-by: agwaman

[pazdera]

Just a note: I explored git-packagebuild a while ago, but I was unable to make it cross-compile for armhfv6. It would be awesome if we could make it work, because for us, cross-compiling for the Raspberry Pi is an essential feature of dr.