bug#18119: df --si misleading output units

[Bob Proulx]

Kernc wrote:
> By example,
> 
> $ df --human-readable /dev/sdb2
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sdb2        82G   66G   12G  86% /home
> $ df --si /dev/sdb2
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sdb2        88G   71G   13G  86% /home
> 
> In both cases, the output unit presented is G(iB) whereas a
> power-of-1000 unit (GB) was requested in the latter invocation.

Saying "G" does not specify either GiB nor GB.  It specifies the
magnitude in the unit requested.  Saying that it specifies GiB in both
cases is incorrect.

If SI powers of ten units were requested then that is emitted.  If
human readable powers of two units were requested then that is
emitted.

Bob