[png-mng-implement] libpng-1.6.31beta05 is available, with eXIf chunk support

[Glenn Randers-Pehrson]

libpng-1.6.31beta05, with eXIf chunk support, is available from
https://ftp-osl.osuosl.org/pub/libpng/src/beta/libpng16
ftp://ftp-osl.osuosl.org/pub/libpng/src/beta/libpng16
http://libpng.download/src/beta/libpng16
and from
http://libpng.sf.net

Version 1.6.31beta05 [July 13, 2017]
Added eXIf chunk support.

Glenn