The 16-bit cases still use "L" as we don't have a 16-bit test system.

to conditions where types that are 32 bits in the GCC 32-bit
world (uLong and png_size_t) become 64 bits in the 64-bit
world.  This produces potential truncation errors which the
compiler correctly flags.

png_XYZ_from_xy_checked

by default.

(Clifford Yap)

to pngpriv.h (functions yet to be implemented).

The "_DLL" is removed from the test of whether a DLL is being built.

and fixed spelling (truely -> truly) in comments.