Add Zorn to HOL-Library

--- a/src/HOL/Library/Library.thy	Tue Nov 26 10:17:14 2013 +0100
+++ b/src/HOL/Library/Library.thy	Tue Nov 26 12:29:31 2013 +0100
@@ -65,6 +65,7 @@
   Transitive_Closure_Table
   Wfrec
   While_Combinator
+  Zorn
 begin
 end
 (*>*)