Hi Guix,

I placed python-pyxdg in the freedesktop module because it fits there
and because it allows me to avoid a circular dependency.

One of the tests is failing.  I do not know why a PNG image is detected
as 'x-apple-ios-png' rather than the expected 'png', but I suspect it's
a problem in "shared-mime-info".  I made the check phase return #t to
avoid a build failure.