Fixing #71342 serializing '\n' in attribute values added a specific test.

* tree.c: Fixing #71342 serializing '\n' in attribute values
* result/noent/att3 result/att3 test/att3: added a specific
  test.
Daniel
diff --git a/result/att3 b/result/att3
new file mode 100644
index 0000000..3f3ac5c
--- /dev/null
+++ b/result/att3
@@ -0,0 +1,2 @@
+<?xml version="1.0"?>
+<select onclick="aaaa&#10;      bbbb&#xA0;">f&#xA0;oo</select>