Log Message:
Update to 1.2.15:

version 1.2.15beta1 [December 3, 2006]
  Generated configure with autoconf-2.61 instead of 2.60
  Revised configure.ac to update libpng.pc and libpng-config.

version 1.2.15beta2 [December 3, 2006]
  Always export MMX asm functions, just stubs if not building pnggccrd.c

version 1.2.15beta3 [December 4, 2006]
  Add "png_bytep" typecast to profile while calculating length in \ 
pngwutil.c

version 1.2.15beta4 [December 7, 2006]
  Added scripts/CMakeLists.txt
  Changed PNG_NO_ASSEMBLER_CODE to PNG_NO_MMX_CODE in scripts, like 1.4.0beta

version 1.2.15beta5 [December 7, 2006]
  Changed some instances of PNG_ASSEMBLER_* to PNG_MMX_* in pnggccrd.c
  Revised scripts/CMakeLists.txt

version 1.2.15beta6 [December 13, 2006]
  Revised scripts/CMakeLists.txt and configure.ac

version 1.2.15rc1 [December 18, 2006]
  Revised scripts/CMakeLists.txt

version 1.2.15rc2 [December 21, 2006]
  Added conditional #undef jmpbuf in pngtest.c to undo #define in AIX headers.
  Added scripts/makefile.nommx

version 1.2.15rc3 [December 25, 2006]
  Fixed shared library numbering error that was intruduced in 1.2.15beta6.

version 1.2.15rc4 [December 27, 2006]
  Fixed handling of rgb_to_gray when png_ptr->color.gray isn't set.

version 1.2.15rc5 [December 31, 2006]
  Revised handling of rgb_to_gray.

version 1.2.15 [January 5, 2007]
  Added some (unsigned long) typecasts in pngtest.c to avoid printing errors.