[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.

pngtest.c

@@ -1726,4 +1726,4 @@ main(int argc, char *argv[])
 }
 
 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef version_1_5_0beta53 your_png_h_is_not_version_1_5_0beta53;
+typedef png_libpng_version_1_5_0beta53 Your_png_h_is_not_version_1_5_0beta53;