fetchFromGitorious: add helper

pkgs/top-level/all-packages.nix

···
     inherit sha256;
   };
 
+  fetchFromGitorious = { owner, repo, rev, sha256, name ? "${repo}-${rev}-src" }: fetchzip {
+    inherit name;
+    url = "https://gitorious.org/${owner}/${repo}/archive/${rev}.tar.gz";
+    inherit sha256;
+  };
+
   resolveMirrorURLs = {url}: fetchurl {
     showURLs = true;
     inherit url;