packagekit: add latest from hughsie's github repo

- currently pulled in from Git until the next release of PackageKit
  has Nix support
- also: add in a service module to start packagekit properly
- nixos service can be enabled via services.packagekit.enable
- packagekit requires nixunstable to build properly

nixos/modules/services/misc/packagekit.nix

@@ -0,0 +1,61 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.services.packagekit;
+
+  backend = "nix";
+
+  packagekitConf = ''
+[Daemon]
+DefaultBackend=${backend}
+KeepCache=false
+    '';
+
+  vendorConf = ''
+[PackagesNotFound]
+DefaultUrl=https://github.com/NixOS/nixpkgs
+CodecUrl=https://github.com/NixOS/nixpkgs
+HardwareUrl=https://github.com/NixOS/nixpkgs
+FontUrl=https://github.com/NixOS/nixpkgs
+MimeUrl=https://github.com/NixOS/nixpkgs
+      '';
+
+in
+
+{
+
+  options = {
+
+    services.packagekit = {
+      enable = mkEnableOption
+        ''
+          PackageKit provides a cross-platform D-Bus abstraction layer for
+          installing software. Software utilizing PackageKit can install
+          software regardless of the package manager.
+        '';
+    };
+
+  };
+
+  config = mkIf cfg.enable {
+
+    services.dbus.packages = [ pkgs.packagekit ];
+
+    systemd.services.packagekit = {
+      description = "PackageKit Daemon";
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig.ExecStart = "${pkgs.packagekit}/libexec/packagekitd";
+      serviceConfig.User = "root";
+      serviceConfig.BusName = "org.freedesktop.PackageKit";
+      serviceConfig.Type = "dbus";
+    };
+
+    environment.etc."PackageKit/PackageKit.conf".text = packagekitConf;
+    environment.etc."PackageKit/Vendor.conf".text = vendorConf;
+
+  };
+
+}