Be pedantically correct about units and scale factors.  There are two
choices: either SI scale factors (k, M, G, T, ...) and scale by 10^3
each step, or IEC (binary) scale factors (Ki, Mi, Gi, Ti, ...) and scale
by 2^10 each step.

File sizes generally use IEC -- KiB, MiB

Bandwidth generally uses SI -- kB/s, MB/s

For ultimate pedantry, bandwith should probably be measured in
bits per secon: kb/s Mb/s but whats a factor of eight between friends?

Fixes: #659
Merge branch 'master' into docco