[devel] Mention zlib-libpng license in each source file
diff --git a/pngwio.c b/pngwio.c
index e89e74b..0e7e8d0 100644
--- a/pngwio.c
+++ b/pngwio.c
@@ -2,11 +2,13 @@
/* pngwio.c - functions for data output
*
* Last changed in libpng 1.4.0 [June 24, 2009]
- * For conditions of distribution and use, see copyright notice in png.h
* Copyright (c) 1998-2009 Glenn Randers-Pehrson
* (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
* (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
*
+ * This code is released under the zlib-libpng license.
+ * For conditions of distribution and use, see copyright notice in png.h
+ *
* This file provides a location for all output. Users who need
* special handling are expected to write functions that have the same
* arguments as these and perform similar functions, but that possibly