Update libpng to 1.6.24

[Karl Harbinger]

The internal libpng code is still a bit old. Can you update it to the recent version 1.6.24?

[imm]

On 11 August 2016 at 14:57, Karl Harbinger wrote:

The internal libpng code is still a bit old. Can you update it to the recent version 1.6.24?

​Well, it is not really *so* old - it is 1.6.16 IIRC, which is not too bad!

We may update, but there is some effort involved and are a very small team, so it is not really a priority for us.

Note that fltk's configure system will try to use a "system" version of the bundled support libs (libz, png, jpeg) if they are found at configure time, in preference​ to the fltk built-in's, unless explicitly told not to.

So the bundled libs are really only there as a last resort for use by devs who do not already have the appropriate libs in place.

I'd imagine all *nix systems, including OSX, probably use the system libs unless told otherwise, and many devs on Windows will also have these libs pre-installed in their work environments too.