if not already defined.

because they were handled improperly by Portland Group's PGI-14.1 - PGI-14.3
when using its "__builtin_pow()" function.

PNG_MAXIMUM_INFLATE_WINDOW option, so #define it out when appropriate in
pngvalid.c

with test programs.

pngvalid.c

this version of pngvalid in libpng 1.5

This reverts to the previous 'static' implementation and works round
the 'unused static function' warning by using PNG_UNUSED().

configurations don't build because of missing contrib/libtests test programs
and overly complex dependencies in scripts/pnglibconf.dfa. This change adds
contrib/conftest/*.dfa files that can be used in automatic build
scripts to ensure that these configurations continue to build.

it can manage, limited by the number of rows.

requirements of png_modifier are greater than that of png_store and as a
consequence compilation of pngvalid.c results in a warning about increased
alignment requirements because of the bare cast to (png_modifier*). The code
is safe, because the pointer is known to point to a stack allocated
png_modifier, but this change avoids the warning.

  Fixed default behavior of ARM_NEON_API. If the ARM NEON API option was
    compiled without the CHECK option it defaulted to on, not off.

  Check user callback behavior in pngunknown.c. Previous versions compiled
    if SAVE_UNKNOWN was not available but did nothing since the callback
    was never implemented.

  Merged pngunknown.c with 1.7 version and back ported 1.7 improvements/fixes

Reverted previous attempt to allow gAMA and sRGB non-support with the
simplified API.

    (Flavio Medeiros).

Folded some long lines.

png_set_* APIs

READ_GAMMA.  Prior to 1.6.0 switching off READ_GAMMA did unpredictable things
to the interfaces that use it (specifically, png_do_background in 1.4 would
simply display composite for grayscale images but do composition
with the incorrect arithmetic for color ones). In 1.6 the semantic
of -DPNG_NO_READ_GAMMA is changed to simply disable any interface that
depends on it; this obliges people who set it to consider whether they
really want it off if they happen to use any of the interfaces in
question (typically most users who disable it won't).