* util/mkisofs/msdos_partition.h: New file (based on
include/grub/msdos_partition.h).
* util/mkisofs/mkisofs.c (use_protective_msdos_label): New variable.
(OPTION_PROTECTIVE_MSDOS_LABEL): New macro.
(ld_options, main): Recognize --protective-msdos-label.
* util/mkisofs/mkisofs.h (use_protective_msdos_label): New declaration.
* util/mkisofs/write.c: Include `"msdos_partition.h"'.
(padblock_write): If `use_protective_msdos_label' is set, patch a
protective DOS-style label in the output image.
* util/grub-mkrescue.in: Use --protective-msdos-label.
