png_set_scale_16_to_8 from pngpriv.h

and fix some other small typos.

    1.5.3beta06
  Also removed a spurious (totally unused and confusing) member from png_info.
  The palette expand optimization prevented expansion to an intermediate RGBA
    form if tRNS was present but alpha was marked to be stripped; this exposed
    a check for tRNS in png_do_expand_palette() which is inconsistent with the
    code elsewhere in libpng.

not libpng version for presence of png_set_chop_16_to_8(), in pngvalid.c

by disabling PNG_CHOP_16_TO_8_SUPPORTED

called.

Fixed some compiliation problems with scaling options.

outside of an unknown-chunk block in png.h because they are also
needed for other uses.

to get the same (inaccurate) output as libpng-1.5.2 and earlier.

and are not necessarily fully supportable, particularly png_strncpy and
png_snprintf.

This allows pngvalid to build when ALPHA_MODE is not supported, which is
required if it is to build on libpng 1.4.

    scripts/makefile.watcom.  This project works with OpenWatcom 1.9. The
    IDE autogenerates appropriate makefiles (libpng.mk) for batch processing.
    The project is configurable, unlike the Visual Studio project, so long
    as the developer has an awk.

    wrong (high by one) 25% of the time. Dividing by 257 with rounding is
    wrong in 128 out of 65536 cases. Getting the right answer all the time
    without division is easy.

only be used to reduce the defined limit, and that it also affects
png writing.

(Bug report by Frank Busse, related to CVE-2004-0421).