[devel] Added the private PNG_UNUSED() macro definition in pngpriv.h.

(adapted from the UNUSED() macro in pngvalid.c by John Bowler)
diff --git a/CHANGES b/CHANGES
index 617e933..bc55f6e 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3089,7 +3089,8 @@
     with pngwio.c and pngwutil.c because the 'write' callback and zlib
     compression both fail to declare their input buffers with 'const'.
 
-Version 1.5.0beta56 [November 25, 2010]
+Version 1.5.0beta56 [December 5, 2010]
+  Added the private PNG_UNUSED() macro definition in pngpriv.h.
 
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