actions for viewing the job status and all builds in a separate base
class that's inherited both by Root.pm and Project.pm so that we get
URIs like /jobstatus and /project/<name>/jobstatus for free.
database queries from a set of jobs that have to be in a release.
E.g. a patchelf release might consist of the jobs "tarball", "build",
and "rpm_fedora10i386". Here the first job ("tarball") is the
primary job: all the others have it as an input. The primary job
supplies the identity of the release.