Log Message:
Update png to 1.2.13 (it fixes CVE-2006-5793).

version 1.2.13beta1 [October 2, 2006]
  Removed AC_FUNC_MALLOC from configure.ac
  Work around Intel-Mac compiler bug by setting PNG_NO_MMX_CODE in pngconf.h
  Change "logical" to "bitwise" throughout documentation.
  Detect and fix attempt to write wrong iCCP profile length.

version 1.0.21, 1.2.13 [November 15, 2006]
  Fix potential buffer overflow in sPLT chunk handler.
  Fix Makefile.am to not try to link to noexistent files.
  Check all exported functions for NULL png_ptr.