fdisk(1) internally uses a signed int. Should a user attempt to specify
a slice containing more than 2^31 - 1 sectors, an error will be reported
on systems with sizeof(long) == 4 and the slice size will be silently
truncated on systems with sizeof(long) > 4.
Instead use an unsigned long to store the slice size in fdisk(1). This
allows the user to specify a slice size up to the maximum permitted by
the MBR on-disk format and does not have any problems with silent
truncation should the use specify an slice size larger than 2^32 on systems
with sizeof(long) > 4.
Submitted by: Mark Johnston (markjdb AT gmail DOT com)
MFC after: 2 weeks
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