enabling subtyping.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@11390 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/tasks/Ant.java

@@ -229,7 +229,7 @@ public class Ant extends Builder {
 
     public static final DescriptorImpl DESCRIPTOR = new DescriptorImpl();
 
-    public static final class DescriptorImpl extends Descriptor<Builder> {
+    public static class DescriptorImpl extends Descriptor<Builder> {
         @CopyOnWrite
         private volatile AntInstallation[] installations = new AntInstallation[0];
 
@@ -238,6 +238,10 @@ public class Ant extends Builder {
             load();
         }
 
+        protected DescriptorImpl(Class<? extends Ant> clazz) {
+            super(clazz);
+        }
+
         protected void convert(Map<String,Object> oldPropertyBag) {
             if(oldPropertyBag.containsKey("installations"))
                 installations = (AntInstallation[]) oldPropertyBag.get("installations");