Add reproducible archive of packages.

Created by: eli-schwartz

This partially subsumes the work of archivetools, in creating the initial packages/${pkgname:0:1}/${pkgname}/${pkgfile} pool every time a package is uploaded. (Archivetools only runs once per day and can miss things.)

And we now also test every package to make sure it can only be db-updated if the archive knows about all packages that were installed in the build environment.