[libpng16] Added #ifdef PNG_READ_SUPPORTED/endif around the

png_chunk_unknown_handling() function, and restored the unknown-chunk
handling code from libpng-1.6.6.

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ANNOUNCE

@@ -27,8 +27,8 @@ Other information:
 Changes since the last public release (1.6.6):
 
 Version 1.6.7 [September 20, 2013]
-  Reverted the change to unknown handling #defines; the change breaks 'NOREAD'
-    builds.
+  Added #ifdef PNG_READ_SUPPORTED/endif around the png_chunk_unknown_handling()
+    function.
 
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CHANGES

@@ -4641,8 +4641,8 @@ Version 1.6.6 [September 20, 2013]
   Removed two stray lines of code from arm/arm_init.c, again.
 
 Version 1.6.7beta01 [September 20, 2013]
-  Reverted the change to unknown handling #defines; the change breaks 'NOREAD'
-    builds.
+  Added #ifdef PNG_READ_SUPPORTED/endif around the png_chunk_unknown_handling()
+    function.
 
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png.c

@@ -855,7 +855,8 @@ png_handle_as_unknown(png_const_structrp png_ptr, png_const_bytep chunk_name)
    return PNG_HANDLE_CHUNK_AS_DEFAULT;
 }
 
-#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
+#ifdef PNG_READ_SUPPORTED
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
 int /* PRIVATE */
 png_chunk_unknown_handling(png_const_structrp png_ptr, png_uint_32 chunk_name)
 {
@@ -864,7 +865,8 @@ png_chunk_unknown_handling(png_const_structrp png_ptr, png_uint_32 chunk_name)
    PNG_CSTRING_FROM_CHUNK(chunk_string, chunk_name);
    return png_handle_as_unknown(png_ptr, chunk_string);
 }
-#endif /* READ_UNKNOWN_CHUNKS */
+#endif /* HANDLE_AS_UNKNOWN */
+#endif /* READ_SUPPORTED */
 #endif /* SET_UNKNOWN_CHUNKS */
 
 #ifdef PNG_READ_SUPPORTED

pngpriv.h

@@ -1431,15 +1431,13 @@ PNG_INTERNAL_FUNCTION(void,png_handle_unknown,(png_structrp png_ptr,
     * just skips the chunk or errors out if it is critical.
     */
 
-#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
-#ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
+#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
 PNG_INTERNAL_FUNCTION(int,png_chunk_unknown_handling,
     (png_const_structrp png_ptr, png_uint_32 chunk_name),PNG_EMPTY);
    /* Exactly as the API png_handle_as_unknown() except that the argument is a
     * 32-bit chunk name, not a string.
     */
-#endif
-#endif /* PNG_READ_UNKNOWN_CHUNKS_SUPPORTED */
+#endif /* PNG_HANDLE_AS_UNKNOWN_SUPPORTED */
 #endif /* PNG_READ_SUPPORTED */
 
 /* Handle the transformations for reading and writing */

pngrutil.c

@@ -2764,7 +2764,6 @@ png_handle_unknown(png_structrp png_ptr, png_inforp info_ptr,
 
    png_debug(1, "in png_handle_unknown");
 
-#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
    /* NOTE: this code is based on the code in libpng-1.4.12 except for fixing
     * the bug which meant that setting a non-default behavior for a specific
     * chunk would be ignored (the default was always used unless a user
@@ -2777,15 +2776,14 @@ png_handle_unknown(png_structrp png_ptr, png_inforp info_ptr,
     * function.
     */
 #  ifndef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
-#     ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
-         keep = png_chunk_unknown_handling(png_ptr, png_ptr->chunk_name);
-#     endif
+   keep = PNG_HANDLE_CHUNK_AS_DEFAULT;
 #  endif
 
    /* One of the following methods will read the chunk or skip it (at least one
     * of these is always defined because this is the only way to switch on
     * PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
     */
+#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
 #  ifdef PNG_READ_USER_CHUNKS_SUPPORTED
       /* The user callback takes precedence over the chunk keep value, but the
        * keep value is still required to validate a save of a critical chunk.
@@ -2893,7 +2891,7 @@ png_handle_unknown(png_structrp png_ptr, png_inforp info_ptr,
 
          png_crc_finish(png_ptr, length);
       }
-#  endif
+#  endif /* PNG_SAVE_UNKNOWN_CHUNKS_SUPPORTED */
 
 #  ifdef PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED
       /* Now store the chunk in the chunk list if appropriate, and if the limits