OS X: Switch to a sane packaging system

The main effect of this patchset is that it switches from the PackageMaker format (*.pmdoc) to a distribution file (in this case distribution.xml) for describing the resulting package. The PackageMaker format is supposed to be opaque, but we were fiddling with it to automatically update the Jenkins version. Also, PackageMaker has a tendency to touch every part of the pmdoc even if only one part was modified.

By using distribution.xml, the packaging is much easier to modify. The actual installation paths are mirrored by the `dest_root` folders, new parts (ex: a future preference pane) can be added easily, and the permissions fixing that had to be handled by post-install scripts is now correctly set by the packaging process.

Potential downsides are the extensive moving this patch did to the code base, and a slightly longer build script.