libfdisk: (sun) fix creation of whole disk partition

libfdisk: (sun) fix creation of whole disk partition

sun_add_partition() allowed the 1st sector to be 0 for the 3rd partition
only if that sector was free or if other partitions covered the whole
disk. Now it's always allowed for the 1st sector to be set to 0 for
the 3rd partition.

[kzak@redhat.com: - print info about "wholedisk" before "First sector" dialog for 3rd partition
                  - default to 0 for 3rd partition start sector]

Signed-off-by: Mikhail Vorobyov <m.vorobyov@cs.msu.ru>
Signed-off-by: Karel Zak <kzak@redhat.com>