[libsigcplusplus/libsigc++-2-10] benchmark: Add copyright header.

[Murray Cumming <murrayc src gnome org>]

commit 6e34e4270a7b6390b1c04f1571bd7f77f81ea412
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Apr 20 09:32:46 2016 +0200

    benchmark: Add copyright header.

 tests/benchmark.cc |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/tests/benchmark.cc b/tests/benchmark.cc
index f75b73c..e4adb3c 100644
--- a/tests/benchmark.cc
+++ b/tests/benchmark.cc
@@ -1,3 +1,7 @@
+/* Copyright 2003 - 2016, The libsigc++ Development Team
+ *  Assigned to public domain.  Use as you wish without restriction.
+ */
+
 #include <iostream>
 #include <sigc++/signal.h>
 #include <sigc++/functors/mem_fun.h>