Changes made to pristine png source by mozilla.org developers.

2008/08/21  -- Synced with libpng-1.2.31 (bug #418900).

2008/03/29  -- Initialize prev_row for each APNG frame, only when
               the frame size increases (bug #420416)

2008/01/18  -- Synced with libpng-1.2.24 (bug #408429).

2007/11/13  -- Synced with libpng-1.2.23; Removed pnggccrd.c and pngvcrd.c;
               Reduced footprint by removing error and warning text
               (bug #403239)

2007/11/06  -- Synced with libpng-1.2.22 (removes MMX support) (bug #386585)

2007/07/27  -- Enabled cHRM and iCCP chunks for color management (bug #16769)

2007/05/05  -- Zeroed png_ptr->num_trans on CRC error (bug #374810)

2007/04/19  -- Synced with libpng-1.2.16 tree (bug #373249)

2007/03/20  -- Added support for APNG (bug #257197)

2006/06/27  -- Synced with libpng-1.2.12 tree (bug #334110)

2004/10/07  -- Synced with libpng-1.2.7 tree (bug #261922)

2004/10/07  -- Added mozpngconf.h (bug #208607)