[libpng16] Changed tabs to 3 spaces in png_debug macros and changed '"%s"m'

to '"%s" m' to improve portability among compilers.
Changed png_free_default() to free() in pngtest.c
[libpng16] Changed deprecated png_free_default() to free() in pngtest.c

Changed tabs to 3 spaces in png_debug macros and changed '"%s"m'
to '"%s" m' to improve portability among compilers.
[libpng16] Imported from libpng-1.6.8beta02.tar
[libpng16] Bump version to 1.6.8beta03
[libpng16] Fixed unused "wrote_question" in non-write pngtest.
[libpng16] Tidied up pngfix inits and fixed non-write pngtest.