sfdisk: use unsigned long long to internally represent sector number

sfdisk: use unsigned long long to internally represent sector number

Unsigned long is only 4 bytes long on i586, which is not enough to
represent sector number on todays large disks. Use unsigned long long,
which is 8 bytes long, to store the sector numbers internally, so that
we could later make some sanity checks and warn the user if the sector
numbers exceed the limits imposed by DOS partition table format.

Signed-off-by: Petr Uzel <petr.uzel@suse.cz>