Solve the problem of "tileset not found" which prevent from launching DF on all Arch Linux based distribution

When detecting that libpng is not in version 1.5, the script will now download and compile a new libgraphics.so from [https://github.com/svenstaro/dwarf_fortress_unfuck] dwarf_fortress_unfunck to replace the old of Dwarf Fortress. It will normally solve all the problems of tileset "not found" on distributions based on arch linux (which have libpng in version 1.6).

The other solution could be to replace for each graphic pack the png by bmp in the init.txt and to symlink art/mouse.png by art/mouse.bmp.
I think the solution I used needs more code and time to download and compile, but is "cleaner" : there is no modification to do when a graphic pack is added or modified.