Primitive streams

[Brian Goetz]

> So instead of stream.sumBy(IntMapper), we already have:
> stream.map(IntMapper).sum(). If the pipeline prefer to use fuzed
> operation, it's an implementation detail.

If we have IntStream, then yes this is most natural.  The sumBy 
suggestion (Don's, I believe) was an alternative in the event we do not 
have IntStream; you can't define sum() on Stream but you can define 
sumBy(IntMapper) on Stream.