applied fix from Mathias Hasselmann about a bug in URI parsing. fix bug

* uri.c: applied fix from Mathias Hasselmann about a bug in URI
  parsing.
* xpath.c: fix bug #61291 the default XML namespace node is
  missing from the namespace axis.
* tree.c: refuse to create namespaces nodes with prefix "xml"
Daniel
diff --git a/tree.c b/tree.c
index d002d7f..395080e 100644
--- a/tree.c
+++ b/tree.c
@@ -132,6 +132,9 @@
     if ((node != NULL) && (node->type != XML_ELEMENT_NODE))
 	return(NULL);
 
+    if ((prefix != NULL) && (xmlStrEqual(prefix, BAD_CAST "xml")))
+	return(NULL);
+
     /*
      * Allocate a new Namespace and fill the fields.
      */