[libpng16] Fixed some spelling errors.
diff --git a/pngwutil.c b/pngwutil.c
index abb63f8..23d6715 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -677,7 +677,7 @@
 
    /* This is an internal error; 'next' must have been NULL! */
    if (output_len > 0)
-      png_error(png_ptr, "error writing ancilliary chunked compressed data");
+      png_error(png_ptr, "error writing ancillary chunked compressed data");
 }
 #endif /* PNG_WRITE_COMPRESSED_TEXT_SUPPORTED */