[png-mng-implement] libpng-1.4.0beta83 and 1.2.41beta01 are available

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

libpng-1.4.0beta83 and libpng-1.2.41beta01 are available from
ftp://ftp.simplesystems.org/pub/png-group/src
and from
http://libpng.sourceforge.net/index.html

libpng-1.4.0beta82 had some missing curley brackets that
caused it to issue bogus warnings about incorrect filter_type
in the IHDR chunk.

libpng-1.4.0beta82 fixes this bug.  libpng-1.2.41beta01 has
the new png_check_IHDR() function, and is made available
for helping debug a problem on the Mac currently being
discussed on png-mng-implement.

Glenn