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

2002/10/03  -- Synced with libpng-1.2.5 tree

2002/10/06  -- OS/2 bustage fix.  IBM compiler defines __IBMCPP__ instead
               of IBMCPP__ (pngconf.h).

2003/06/11  -- add mozpngconf.h (bug 208607)

2003/07/03  -- enable PNG_NO_WRITE_SUPPORTED in mozpngconf.h (bug 208607)

2003/07/29  -- Add "moz_" decoration on exported symbols (bug 181936).  Set
               "PNG_NO_GLOBAL_ARRAYS" to reduce number of exported symbols.
               Remove some legacy (1.0.x) code from png.c and pngread.c