middleware/file: fix delegations (#376)

Fix the delegation handling in the *file* and *dnssec* middleware.
Refactor tests a bit and show that they are failling.

Add a Tree printer, cleanups and tests.
Fix wildcard test - should get no answer from empty-non-terminal

middleware/file/tree/less_test.go

@@ -65,7 +65,7 @@ Tests:
 		sort.Sort(set(test.in))
 		for i := 0; i < len(test.in); i++ {
 			if test.in[i] != test.out[i] {
-				t.Errorf("test %d: expected %s, got %s\n", j, test.out[i], test.in[i])
+				t.Errorf("Test %d: expected %s, got %s\n", j, test.out[i], test.in[i])
 				n := ""
 				for k, in := range test.in {
 					if k+1 == len(test.in) {