Code freeze break for gnome-desktop

[Matthias Clasen <matthias clasen gmail com>]

I'd like to commit the patch in
https://bugzilla.gnome.org/show_bug.cgi?id=629231 to fix some problems
with mime type handling in the thumbnail code in gnome-desktop. As
things currently are, we get false negatives for some types of icons,
e.g .ico, since the code doesn't take mime type aliasing into account.
The patch has been verified by the bug reporter to fix the problem.

Matthias