[libpng17] Merge recent changes to the manual and pngrutil.c from libpng-1.6.14beta04.
[libpng17] Imported from libpng-1.7.0beta36.tar
[libpng17] Bump version to 1.7.0beta37
[libpng17] Merge pngvalid.c with libpng-1.6.14beta04.
[libpng17] Merge pngvalid.c and pngfix.c with libpng-1.6.14beta04
[libpng17] Merged scripts/* with libpng-1.6.14beta04.
[libpng17] Imported from libpng-1.7.0beta37.tar
[libpng17] Bump version to libpng-1.7.0beta38.tar