Fix 'fdisk -u', a.k.a. MBR_pcopy(), on sparc64 and possibly others.

Fix 'fdisk -u', a.k.a. MBR_pcopy(), on sparc64 and possibly others.

gcc's built-in/in-lined memcpy() can't copy elements of a struct
dos_partiton array from inside the __packed struct dos_mbr into an
'unpacked' local variable. But copying the whole array works fine. Be
consistant and use the same idiom in both places the partition table
is parsed.

Leave the landisk workaround/hack in place until it can be confirmed
it is no longer needed.

ok martynas@ after many alternatives crashed and burned.