[libpng15] Imported from libpng-1.5.17rc01.tar
[libpng15] Imported from libpng-1.5.17rc02.tar
[libpng15] Bump version to 1.5.17rc03
[libpng15] Fix spelling of "doclifter" in CHANGES and ANNOUNCE
[libpng15] Fix spelling of "doclifter" in CHANGES and ANNOUNCE