vmstat si and so fields zero with -S mM 1

vmstat si and so fields zero with -S mM 1

'si' and 'so' values depend on the result of the unitConvert
function where the output is a fixed-point size of kb_per_page
after the conversion. It gives 4 for kB units and 0 for MB units.
This also causes problems when switching between 'K' and 'k'
since the output value is 4 in both cases and the result for
'k' and 'K' then doesn't differ ... I swapped the conversion with
multiplication in order to make the number higher so it doesn't
lose precision. Since the unitConvert now accepts long instead
of int, I had to change the input type from int to long.

Signed-off-by: Craig Small <csmall@enc.com.au>