[Tux4kids-discuss] Modern libpng in t4k_common

[LM]

Cheezmeister wrote:
> I found a few minutes to play with T4K and ran into a compiler error on
> our use of the `png_info` struct:
> http://stackoverflow.com/questions/10507610/libpng-1-5-10-error-dereferencing-pointer-to-incomplete-type

I'm building t4k_common with version 1.6.x of libpng and not having
any build issues.  At this point I have several modifications to
t4k_common to add SDL2 support, to try to get it to work better with
tuxtype and not just tuxmath and to fix some internationalization
issues.