Update libpng to current version
|Reported by:||ekdahl||Owned by:||axeld|
|Has a Patch:||no||Platform:||All|
The attached diff contains the update to libpng 1.2.18 which e.g. fixes a couple of vulnerabilities. It seems to work just fine here. There are duplicate png.h and pngconf.h in the libs/png directory which are not needed and can be deleted. The same applies to zlib.