RFR 8022318: Document Spliterator characteristics and binding policy of java util concurrent collection impls

[Paul Sandoz]

Hi,

The following patch updates documentation for various spliterators in the j.u.concurrent package:

  http://cr.openjdk.java.net/~psandoz/tl/JDK-8022318-concurrent-split-docs/webrev/

This syncs from the 166 repo and the documentation is just clarifying stuff that was missing.  Many thanks to Martin for helping out with this.

There are a few additional tweaks here and there that are included, the only non-formating/non-documentation tweak is to SynchronousQueue.iterator():

-    @SuppressWarnings("unchecked")
     public Iterator<E> iterator() {
-        return (Iterator<E>) EmptyIterator.EMPTY_ITERATOR;
-    }
-
-    // Replicated from a previous version of Collections
-    private static class EmptyIterator<E> implements Iterator<E> {
-        static final EmptyIterator<Object> EMPTY_ITERATOR
-            = new EmptyIterator<Object>();
-
-        public boolean hasNext() { return false; }
-        public E next() { throw new NoSuchElementException(); }
-        public void remove() { throw new IllegalStateException(); }
+        return Collections.emptyIterator();
     }

Paul.