xz-utils is part of system and enough distfiles are xz-compressed that
we should have it in stage1 to avoid stage2 dying because someone forgot
to add it to DEPEND.

Please test this patch by applying it your snapshot cache and building a
stage1 and stage2 and confirming that xz-utils is built during stage1.

Index: default/linux/packages.build
===================================================================
RCS file: /var/cvsroot/gentoo-x86/profiles/default/linux/packages.build,v
retrieving revision 1.10
diff -u -B -r1.10 packages.build
--- default/linux/packages.build	24 Nov 2012 21:15:48 -0000	1.10
+++ default/linux/packages.build	26 Jul 2013 03:56:45 -0000
@@ -10,6 +10,7 @@
 
 app-arch/bzip2
 app-arch/gzip
+app-arch/xz-utils
 app-arch/tar
 app-shells/bash
 net-misc/rsync