assorted fixes to python packages

I use those two packages (xdg and rsvg) in the Omaha board-game GUI
(http://repo.or.cz/w/omaha.git). The first patch fixes a blocking bug, and the second one allows to simply install python-rsvg withou having to install a completely unneeded gnome.

What's next with those packages: we should update pyxdg to the latest version (I'll give it a run later), and building python-rsvg should not even require that we build all that gnome stuff, but that is an upstream issue: maybe we could still make a specific recipe which only builds rsvg from the package, and have gnome-python-desktop RDEPEND on it ?