the useful side effect of avoiding a bogus warning generated by the latest
version of the Intel C compiler (it objects to
condition ? string-literal : string-literal).
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
