allow plugins to define its own converter or register aliases.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@6392 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/model/Hudson.java

@@ -2117,7 +2117,7 @@ public final class Hudson extends View implements ItemGroup<TopLevelItem>, Node,
     /**
      * Thread-safe reusable {@link XStream}.
      */
-    private static final XStream XSTREAM = new XStream2();
+    public static final XStream XSTREAM = new XStream2();
 
     /**
      * Thread pool used to load configuration in parallel, to improve the start up time.