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

2009/02/19  -- Synced with libpng-1.2.35 tree

2007/05/05  -- Zero png_ptr->num_trans on CRC error (bug 374810)
 
2004/10/07  -- Synced with libpng-1.2.7 tree

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

2006/09/22  -- fix security problem with too-small error message buffer

2006/09/22  -- fix security problem with too-small gamma-shift array.