RFR: jsr166 jdk9 integration wave 13

[Martin Buchholz]

I see that SpliteratorTraversingAndSplittingTest tests far more collection
implementations than Collection8Test does, but we now have tests that
caught spliterator bugs not caught by
SpliteratorTraversingAndSplittingTest.  Our tests of Spliterators are often
comingled with other test methods, e.g. in testIteratorEquivalence.

So, possible future work: testing could be improved in both dimensions of
increasing number of implementations and increasing number of tests.