empty non-terminal support

When looking for a name in tree, return wether we got to a longer one -

if so we had an ent. Add tests + dnssec tests and refactor the tests as

well a bit.

middleware/file/tree/all.go

@@ -19,3 +19,30 @@ func (n *Node) all(found []*Elem) []*Elem {
 	}
 	return found
 }
+
+// Do performs fn on all values stored in the tree. A boolean is returned indicating whether the
+// Do traversal was interrupted by an Operation returning true. If fn alters stored values' sort
+// relationships, future tree operation behaviors are undefined.
+func (t *Tree) Do(fn func(e *Elem) bool) bool {
+	if t.Root == nil {
+		return false
+	}
+	return t.Root.do(fn)
+}
+
+func (n *Node) do(fn func(e *Elem) bool) (done bool) {
+	if n.Left != nil {
+		done = n.Left.do(fn)
+		if done {
+			return
+		}
+	}
+	done = fn(n.Elem)
+	if done {
+		return
+	}
+	if n.Right != nil {
+		done = n.Right.do(fn)
+	}
+	return
+}