upgrade cairo, pixman and libpng to the latest

The latest versions, libpng-1.6.5, pixman-0.30.2 and cairo-1.12.16 are used here.

All Cairo samples seem to work *EXCEPT* when using SVG on x86_64 which renders an all-white texture.
jump from libpng 1.4 to 1.6
upgrade cairo samples to build fat and link to libpng16.a