updated the policy on private mail answers more work on Relax-NG

* README: updated the policy on private mail answers
* relaxng.c: more work on Relax-NG
* test/relaxng/* result/relaxng/*: augmented/updated the
  regression tests
Daniel
diff --git a/test/relaxng/tutor5_3.rng b/test/relaxng/tutor5_3.rng
new file mode 100644
index 0000000..e49f6ec
--- /dev/null
+++ b/test/relaxng/tutor5_3.rng
@@ -0,0 +1,6 @@
+<element name="bad" xmlns="http://relaxng.org/ns/structure/1.0">
+  <data type="string"/>
+  <element name="note">
+    <text/>
+  </element>
+</element>