Add latest version of xz (#2916)

var/spack/repos/builtin/packages/xz/package.py

@@ -32,6 +32,8 @@ class Xz(AutotoolsPackage):
        the successor to LZMA Utils."""
     homepage = "http://tukaani.org/xz/"
     url      = "http://tukaani.org/xz/xz-5.2.0.tar.bz2"
+    list_url = "http://tukaani.org/xz/old.html"
 
-    version('5.2.0', '867cc8611760240ebf3440bd6e170bb9')
+    version('5.2.3', '1592e7ca3eece099b03b35f4d9179e7c')
     version('5.2.2', 'f90c9a0c8b259aee2234c4e0d7fd70af')
+    version('5.2.0', '867cc8611760240ebf3440bd6e170bb9')