Stream constructors for stream(Iterator) in StreamSupport?

[Brian Goetz]

Currently StreamSupport contains seq/par versions of
   stream(Spliterator)
   stream(Supplier<Spliterator>)
for ref/int/long/double.

In java.util.Spliterators, there are adapters to turn an Iterator into a 
Spliterator.

I think we should add convenience factories for

   stream(Iterator)

to StreamSupport as well.