Allow process() to throw Throwable, which we catch anyway.

jetty-util/src/main/java/org/eclipse/jetty/util/IteratingCallback.java

@@ -156,9 +156,9 @@ public abstract class IteratingCallback implements Callback
      *
      * @return the appropriate Action
      *
-     * @throws Exception if the sub task processing throws
+     * @throws Throwable if the sub task processing throws
      */
-    protected abstract Action process() throws Exception;
+    protected abstract Action process() throws Throwable;
 
     /**
      * Invoked when the overall task has completed successfully.