added a convenience class

core/src/main/java/hudson/util/CompoundEnumeration.java

+package hudson.util;
+
+import java.util.Arrays;
+import java.util.Enumeration;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * {@link Enumeration} that aggregates multiple {@link Enumeration}s.
+ *
+ * @author Kohsuke Kawaguchi
+ */
+public class CompoundEnumeration<T> implements Enumeration<T> {
+    private final Iterator<Enumeration<? extends T>> base;
+
+    private Enumeration<? extends T> cur;
+
+    public CompoundEnumeration(Enumeration... e) {
+        this((Iterable)Arrays.asList(e));
+    }
+
+    public CompoundEnumeration(Iterable<Enumeration<? extends T>> e) {
+        this.base = e.iterator();
+    }
+
+    public boolean hasMoreElements() {
+        while (!cur.hasMoreElements() && base.hasNext()) {
+            cur = base.next();
+        }
+        return cur.hasMoreElements();
+    }
+
+    public T nextElement() throws NoSuchElementException {
+        return cur.nextElement();
+    }
+}
+