[libpng17] Fixed default behavior of ARM_NEON_API. If the ARM NEON API option is

compiled without the CHECK option it defaulted to on, not off.
[libpng17] Catch up with recent libpng16 changes; unknown handling and spelling

corrections
[libpng17] Updated pngunknown.c
[libpng17] Checked in missing update to pnglibconf.dfa