boosting common commnent parsing code, it was really slow. added sprecific

* parser.c: boosting common commnent parsing code, it was really
  slow.
* test/comment[3-5].xml result//comment[3-5].xml*: added sprecific
  regression tests
Daniel
diff --git a/test/comment4.xml b/test/comment4.xml
new file mode 100644
index 0000000..93282d8
--- /dev/null
+++ b/test/comment4.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="ISO-8859-1"?>
+<!-- test of non ascii comments like là et très -->
+<!--à another one -->
+<!-- another one à-->
+<doc/>