gnome3.nautilus: add thumbnailers

Nautilus, resp. gnome-desktop, scans `thumbnailers` directories
under the paths in `XDG_DATA_DIRS`. gdk-pixbuf was not, for some
reason, listed in the variable, therefore Nautilus did not generate
image thumbnails.

I also add librsvg to the variable so that SVG files can be rendered.
It does not work at the moment, though, because of incorrect path to
the renderer.

pkgs/desktops/gnome-3/core/nautilus/default.nix

@@ -1,6 +1,6 @@
 { stdenv, fetchurl, pkgconfig, libxml2, dbus_glib, shared_mime_info, libexif
 , gtk, gnome3, libunique, intltool, gobjectIntrospection, gnome-autoar, glib
-, libnotify, wrapGAppsHook, exempi, librsvg, tracker, libselinux }:
+, libnotify, wrapGAppsHook, exempi, librsvg, tracker, libselinux, gdk_pixbuf }:
 
 stdenv.mkDerivation rec {
   inherit (import ./src.nix fetchurl) name src;
@@ -16,6 +16,14 @@ stdenv.mkDerivation rec {
   # fatal error: gio/gunixinputstream.h: No such file or directory
   NIX_CFLAGS_COMPILE = "-I${glib.dev}/include/gio-unix-2.0";
 
+  preFixup = ''
+    gappsWrapperArgs+=(
+      # Thumbnailers
+      --prefix XDG_DATA_DIRS : "${gdk_pixbuf}/share"
+      --prefix XDG_DATA_DIRS : "${librsvg}/share"
+    )
+  '';
+
 #  hardeningDisable = [ "format" ];
   enableParallelBuilding = true;