[devel] Revised and renamed the typedef in png.h and png.c that was designed

to catch library and header mismatch, also found at the end of pngtest.c.
diff --git a/CHANGES b/CHANGES
index 6f88ecb..6912f5c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3067,6 +3067,8 @@
   Use document name "libpng.txt" instead of "libpng-version.txt" as it was
     prior to libpng-1.2.16beta2, to simplify version differences.
   Removed obsolete remarks about setjmp handling from INSTALL.
+  Revised and renamed the typedef in png.h and png.c that was designed
+    to catch library and header mismatch.
 
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