[libpng16] Improved pngstest speed by not doing redundant tests and add const

to the background parameter of png_image_finish_read. The --background
option is now done automagically only when required, so that commandline
option no longer exists.
diff --git a/CHANGES b/CHANGES
index f6ccee0..affd6e8 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3901,6 +3901,10 @@
   Moved automake options to AM_INIT_AUTOMAKE in configure.ac
   Added color-tests, silent-rules (Not yet implemented in Makefile.am) and
     version checking to configure.ac
+  Improved pngstest speed by not doing redundant tests and add const to
+    the background parameter of png_image_finish_read. The --background
+    option is now done automagically only when required, so that commandline
+    option no longer exists.
 
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