[libpng15] Quiet an uninitialized memory warning from VC2013 in png_get_png().
[libpng15] Imported from libpng-1.5.18rc02.tar
[libpng15] Updated documentation about sCAL chunk support.
[libpng15] Imported from libpng-1.5.18.tar
[libpng15] Bump version to 1.5.19beta01