Add a copyright notice to treeplot

treeplot

@@ -2,6 +2,14 @@
 #
 # Create a graph of patch flow into the mainline.
 #
+# This code is part of the LWN git data miner.
+#
+# Copyright 2007-8 LWN.net
+# Copyright 2007-8 Jonathan Corbet <corbet@lwn.net>
+#
+# This file may be distributed under the terms of the GNU General
+# Public License, version 2.
+#
 import sys
 import patterns