to see if that works better for the auto-license-detectors

outside of the PNG_READ|WRITE_ANCILLARY_CHUNK_SUPPORTED blocks, where
they did not really belong.  Updated CHANGES and ANNOUNCE.

It is not of any use in libpng-1.4.0; it was only to support binary
compatibility between some old libpng-1.0.x versions.  It should have
been removed from libpng-1.2.x as well but it is too late for that now.

    to "#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED", to make the png_set_keep
    mechanism available for ignoring known chunks even when not saving
    unknown chunks.

about calling png_set_IHDR() multiple times and about the order
of color samples in the tRNS chunk.

about calling png_set_IHDR() multiple times and about the order
of color samples in the tRNS chunk.

about using png_set_io_ptr() in configure scripts for detecting libpng

Broke several remaining "if () statement;" and "else statement;" into
two lines.

since there's only one makefile, so users can just type "make"
instead of "make -f makefile.std".

based on contrib/gregbook/rpng2-x

png_combine_row() and png_read_finish_row() are not used by progressive
PNG readers.

This should be handled in the APNG fork instead of in libpng proper.
This reverts commit ee59a9f9.

This forces the prev_row array to be cleared before the first
row of each image and interlace pass.