fixed a possible infinite loop. This doesn't eliminate the possibility that context classloader has UberClassLoader as an ancestor, but it fixes the problem Rama is seeing.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@8868 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/PluginManager.java

@@ -148,7 +148,7 @@ public final class PluginManager {
             // first, use the context classloader so that plugins that are loading
             // can use its own classloader first.
             ClassLoader cl = Thread.currentThread().getContextClassLoader();
-            if(cl!=null)
+            if(cl!=null && cl!=this)
                 try {
                     return cl.loadClass(name);
                 } catch(ClassNotFoundException e) {