The scale factor has to be considered in the multiplication because
many algorithms will depend of the precision configured in the scale,
that, until now, was considered only for division. BSD and Plan9
dc differ about how to handle this, and plan9 always use only the
scale factor, while BSD uses the maximun of the scale factor or the
bigger scale of the operands. The second seems more sensible and
produces output that user would expect, for example 0k 0.5 0.5*p would
produce 0.2 with the BSD criteria, but it would generate 0 with the
plan9 criteria.
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