[png-mng-implement] libpng-1.6.0beta25 is available

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

libpng-1.6.0beta25 is available from the usual places.

Version 1.6.0beta25 [June 16, 2012]
  Revised png_set_keep_unknown_chunks() so num_chunks < 0 means ignore all
    unknown chunks and all known chunks except for IHDR, PLTE, tRNS, IDAT,
    and IEND.  Previously it only meant ignore all unknown chunks, the
    same as num_chunks == 0. Revised png_image_skip_unused_chunks() to
    provide a list of chunks to be processed instead of a list of chunks to
    ignore.  Revised contrib/gregbook/readpng2.c accordingly.

Glenn