xz and tar.xz archives should each have their own icons to differentiate them from other archive formats. The current situation: * There are no icons for application/x-xz which is the mimetype for xz archives on my system. * There are icons for application/x-xz-pkg which are merely symlinks to package-x-generic * There are icons for application/x-xz-compressed-tar which are merely symlinks to application/x-compressed-tar (tar.gz)