jackmix: Build jackmix in two flavours

Flavours are:
- *jackmix* using jack2 (default)
- *jackmix_jack1* using jack1

pkgs/applications/audio/jackmix/default.nix

···
-{ stdenv, fetchurl, pkgs }:
+{ stdenv, fetchurl, pkgs, jack ? pkgs.libjack2 }:
 
 stdenv.mkDerivation rec {
   name = "jackmix-0.5.2";
···
     pkgs.pkgconfig
     pkgs.scons
     pkgs.kde4.qt4
-    pkgs.jack1
     pkgs.lash
-    pkgs.libuuid # should be a propagatedBuildInput on jack1
+    jack
   ];
 
   buildPhase = ''

pkgs/top-level/all-packages.nix

···
   jackmeter = callPackage ../applications/audio/jackmeter { };
 
   jackmix = callPackage ../applications/audio/jackmix { };
+  jackmix_jack1 = jackmix.override { jack = jack1; };
 
   jalv = callPackage ../applications/audio/jalv { };