chunk handling and transform rewrite

This implements a new chunk parse implementation that can be shared, it
is currently shared by the progressive reader and the sequential one
(not, yet, the writer).

The patch also implements shared transform handling that is used
throughout.

Signed-off-by: John Bowler <jbowler@acm.org>

example.c

@@ -524,7 +524,7 @@ void read_png(FILE *fp, int sig_read)  /* File is already open */
    /* Add filler (or alpha) byte (before/after each RGB triplet) */
    png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);
 
-#ifdef PNG_READ_INTERLACING_SUPPORTED
+#ifdef PNG_READ_DEINTERLACE_SUPPORTED
    /* Turn on interlace handling.  REQUIRED if you are not using
     * png_read_image().  To see how to handle interlacing passes,
     * see the png_read_row() method below:
@@ -532,7 +532,7 @@ void read_png(FILE *fp, int sig_read)  /* File is already open */
    number_passes = png_set_interlace_handling(png_ptr);
 #else
    number_passes = 1;
-#endif /* READ_INTERLACING */
+#endif /* READ_DEINTERLACE */
 
 
    /* Optional call to gamma correct and add the background to the palette
@@ -715,7 +715,7 @@ row_callback(png_structp png_ptr, png_bytep new_row,
     */
    png_bytep old_row = ((png_bytep *)our_data)[row_num];
 
-#ifdef PNG_READ_INTERLACING_SUPPORTED
+#ifdef PNG_READ_DEINTERLACE_SUPPORTED
    /* If both rows are allocated then copy the new row
     * data to the corresponding row data.
     */
@@ -744,7 +744,7 @@ row_callback(png_structp png_ptr, png_bytep new_row,
     * to pass the current row as new_row, and the function will combine
     * the old row and the new row.
     */
-#endif /* READ_INTERLACING */
+#endif /* READ_DEINTERLACE */
 }
 
 end_callback(png_structp png_ptr, png_infop info)