[png-mng-implement] Libpng-1.2.24rc01 available

[Glenn Randers-P. <gl...@gm...>]

Libpng-1.2.24rc01 is available at
ftp://ftp.simplesystems.org/pub/png-group/src
and at
http://libpng.sf.net

The only changes are some minor revisions to the contrib/pngminim
makefiles, to avoid compiling unused files.

Glenn