[OE-core] libpng update to 1.5.13 V2

[Marko Lindqvist]

In openembedded-core itself, libmatchbox does not compile
against libpng15. Patch for that sent already.

In meta-openembedded, libsdl-image is known not to compile
against libpng15. Patch for that too sent already.

I have not been systematically testing build of all the
possible components. Above two problems are just the ones
I've encountered as part of my typical builds.


 - ML