just trying chmod u+w alone is pointless unless we retry removal.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@5367 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/Util.java

@@ -137,8 +137,8 @@ public class Util {
                 LOGGER.log(Level.INFO,"Failed to chmod "+f,e);
             }
 
-            throw new IOException("Unable to delete " + f.getPath());
-
+            if(!f.delete() && f.exists())
+                throw new IOException("Unable to delete " + f.getPath());
         }
     }