anchor.diff:    allPackages = import ./all-packages.nix;
   
     pkgs = allPackages {};
  +
  +  /* Set the Hydra scheduling priority for a job.  The default
  +     priority (100) should be used for most jobs.  A different
  +     priority should only be used for a few particularly interesting
  +     jobs (in terms of giving feedback to developers), such as stdenv.
  +  */
  +  prio = level: job: toJob job // { schedulingPriority = level; };
  +
  +  toJob = x: if builtins.isAttrs x then x else
  +    { type = "job"; systems = x; schedulingPriority = 100; };
   
     /* Perform a job on the given set of platforms.  The function `f' is
        called by Hydra for each platform, and should return some job
  
positive.code:   splashutils_15 = linux;
    sqlite = allBut "i686-cygwin";
    ssmtp = linux;
    strace = linux;
    su = linux;
    subversion = all;
  
negative.code: 
    /* Map an attribute of the form `foo = [platforms...]'  to `testOn
       [platforms...] (pkgs: pkgs.foo)'. */
    mapTestOn = pkgs.lib.mapAttrsRecursiveCond
      (as: !(as ? type && as.type == "job"))
      (path: value:
        let
          job = toJob value;
          getPkg = pkgs:
            pkgs.lib.addMetaAttrs { schedulingPriority = toString job.schedulingPriority; }
            (pkgs.lib.getAttrFromPath path pkgs);
        in testOn job.systems getPkg);
  
    /* Common platform groups on which to test packages. */
    linux = ["i686-linux" "x86_64-linux"];
  