busybox:
 * add explicit xz support, backport of this upstream commit http://git.busybox.net/busybox/commit?id=dfc2473b9ed88039697ac89ee2a4301cdaefcf84


git-svn-id: file:///var/svn/freetz/trunk@9993 149334a1-2f27-0410-a3b9-fc62619ac1e6