libfdisk: make yes/no dialogs more robust

Signed-off-by: Karel Zak <kzak@redhat.com>
sfdisk: require confirmation before write to the device

Signed-off-by: Karel Zak <kzak@redhat.com>
libfdisk: add fdisk_copy_parttype()

Signed-off-by: Karel Zak <kzak@redhat.com>
sfdisk: support -N for primary partitions

Signed-off-by: Karel Zak <kzak@redhat.com>