librsvg: propagate glib and gtk

svn path=/nixpkgs/trunk/; revision=25866

pkgs/desktops/gnome-2.28/desktop/librsvg/default.nix

···
     url = mirror://gnome/sources/librsvg/2.26/librsvg-2.26.0.tar.bz2;
     sha256 = "1sivagvlyr58hxgazr6pyq3yfxbg0wrv7rgzsk5xi631v3qbbjpx";
   };
-  buildInputs = [ pkgconfig libxml2 libgsf bzip2 glib gtk libcroco ];
+  buildInputs = [ pkgconfig libxml2 libgsf bzip2 libcroco ];
+  propagatedBuildInputs = [ glib gtk ];
 }