fdisk: offer aligned first sector

fdisk: offer aligned first sector

Typical "new partition" dialog looks like:

     Partition number (1-4): 1
     First sector (4-818687, default 4):
                             ^^^^^^^^^

The range (e.g. 4-818687) depends on fdisk mode (DOS/non-DOS), but the
default value should be always aligned.

For example RAID5 device in the DOS mode:

   Disk /dev/md0: 419 MB, 419168256 bytes
   2 heads, 4 sectors/track, 102336 cylinders, total 818688 sectors
   Units = sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 65536 bytes
   Disk identifier: 0x081479c3

   ....

   Command (m for help): n
   Command action
      e   extended
      p   primary partition (1-4)
   p
   Partition number (1-4): 1
   First sector (4-818687, default 128):    <---- !!!
   Using default value 128
   Last sector, +sectors or +size{K,M,G} (128-818687, default 818687): +10M

   Command (m for help): p

   ....

       Device Boot      Start         End      Blocks   Id  System
   /dev/md0p1             128       20607       10240   83  Linux

For non-DOS mode the range will be:

   First sector (128-818687, default 128):

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