Spliterators of iterators

[Martin Buchholz]

Staring at LinkedTransferQueue.java, I see:

                    return Spliterators.spliterator
                        (a, 0, i, (Spliterator.ORDERED |
                                   Spliterator.NONNULL |
                                   Spliterator.CONCURRENT));

but ... that's a spliterator over an immutable array, so shouldn't we have
IMMUTABLE instead of CONCURRENT?

Looking further, I see ArraySpliterator requires its input array to be
unmodified during operation

         * @param array the array, assumed to be unmodified during use

("assumed" is weird in javadoc.  maybe "required"?)

but ArraySpliterator does not include IMMUTABLE in characteristics, even
though Arrays.spliterator does.

I suggest fixing all these array spliterator characteristics to always
report IMMUTABLE and never report CONCURRENT, and to document this fact, as
we already do with SIZED and SUBSIZED.