issue validation status on stderr, not stdout as suggested by Pawel

* xmllint.c: issue validation status on stderr, not stdout as suggested
  by Pawel Palucha
* result/relaxng/*: this change slightly all the output from RNG
  regressions.
Daniel
diff --git a/result/relaxng/demo2_err b/result/relaxng/demo2_err
index e69de29..9bdaeb9 100644
--- a/result/relaxng/demo2_err
+++ b/result/relaxng/demo2_err
@@ -0,0 +1 @@
+./test/relaxng/demo2.rng validates