Merge branch 'staging' (older one)

Hydra seems OK-ish, except that some aarch64 jobs need restarting
after qt4 timing out for the first time:
https://hydra.nixos.org/eval/1412641?compare=1412561

pkgs/misc/emulators/retroarch/cores.nix

@@ -26,6 +26,8 @@ let
         --add-flags "-L $COREDIR/${d2u core}_libretro.so $@"
     '';
 
+    enableParallelBuilding = true;
+
     passthru = {
       core = core;
       libretroCore = "/lib/retroarch/cores";

pkgs/misc/emulators/retrofe/default.nix

@@ -65,7 +65,7 @@ stdenv.mkDerivation rec {
   postInstall = ''
     wrapProgram "$out/bin/retrofe" \
       --prefix GST_PLUGIN_PATH : "$GST_PLUGIN_SYSTEM_PATH_1_0" \
-      --set    RETROFE_PATH      "\''${RETROFE_PATH:-\$PWD}"
+      --run 'export RETROFE_PATH=''${RETROFE_PATH:-$PWD}'
   '';
 
   meta = with stdenv.lib; {