Log Message:
update to libpng-1.2.6rc2

changes:
version 1.2.6rc2 [August 8, 2004]
  Revised makefile.darwin and makefile.solaris.  Removed makefile.macosx.
  Revised pngtest's png_debug_malloc() to use png_malloc() instead of
     png_malloc_default() which is not supposed to be exported.
  Fixed off-by-one error in one of the conversions to PNG_ROWBYTES() in
     pngpread.c.  Bug was introduced in 1.2.6rc1.
  Fixed bug in RGB to RGBX transformation introduced in 1.2.6rc1.
  Fixed old bug in RGB to Gray transformation.
  Fixed problem with 64-bit compilers by casting arguments to abs()
    to png_int_32.
  Changed "ln -sf" to "ln -f -s" in three makefiles \ 
(solaris, sco, so9).
  Changed "HANDLE_CHUNK_*" to "PNG_HANDLE_CHUNK_*" (Cosmin)
  Added "-@/bin/rm -f $(DL)/$(LIBNAME).so.$(PNGMAJ)" to 15 *NIX makefiles.
  Added code to update the row_info->colortype in png_do_read_filler() (MSB).