[png-mng-implement] libpng-1.2.22beta3 available

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

Libpng-1.2.22beta3 is available at
ftp://ftp.simplesystems.org/pub/png-group/src
and at
http://libpng.sf.net

Fixed the off-by-one offsets after png_strlen().

Removed version and date clutter from the new diff file.

Dmitri,  I did not see your report about '\0' vs 0 in time, but I agree.
I'll fix that in the next upload.

Glenn