Upgrade to libpng 1.6.29

[jdemeyer]

Tarball: http://download.sourceforge.net/libpng/libpng-1.6.29.tar.gz

Depends on #22163

CC: @jpflori @frederichan-IMJPRG

Component: packages: standard

Keywords: atelierpari2017

Author: Jeroen Demeyer, Jean-Pierre Flori

Branch/Commit: aa28f4c

Reviewer: Jean-Pierre Flori, Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/22159

[jdemeyer]

Branch: u/jdemeyer/upgrade_to_latest_libpng

[sagetrac-git]

Commit: f8bbf69

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

f8bbf69

Upgrade to libpng-1.6.28

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

7467913

Upgrade to libpng-1.6.28

[sagetrac-git]

Changed commit from f8bbf69 to 7467913

[jpflori]

Reviewer: Jean-Pierre Flori

[jpflori]

comment:5

Looks good to me.
Let the patchbots do their job.

[jdemeyer]

Dependencies: #22163