Restore BL's authorship attribution, and add "The Jsoncpp Authors" where it was missing.

Requested/noticed in https://github.com/open-source-parsers/jsoncpp/pull/610, and a
followup to https://github.com/open-source-parsers/jsoncpp/pull/607 .
diff --git a/test/cleantests.py b/test/cleantests.py
index 6a441dc..36d5b9b 100644
--- a/test/cleantests.py
+++ b/test/cleantests.py
@@ -1,4 +1,4 @@
-# Copyright 2007 The JsonCpp Authors
+# Copyright 2007 Baptiste Lepilleur and The JsonCpp Authors
 # Distributed under MIT license, or public domain if desired and
 # recognized in your jurisdiction.
 # See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE