Add a redirect to the evaluation page of a view result

E.g.

  http://hydra.nixos.org/view/nixpkgs/unstable/latest/eval

Thus this is the channel representing the latest Nixpkgs for which the
elements of the view "unstable" succeeded:

  http://hydra.nixos.org/view/nixpkgs/unstable/latest/eval/channel

src/lib/Hydra/Helper/Nix.pm

@@ -216,6 +216,7 @@ sub getViewResult {
         , jobs => [@jobs]
         , status => $status
         , timestamp => $timestamp
+        , eval => $ev
         };
 }