concurrent sets

[Doug Lea]

I'm still working on lambda-related tie-ins for j.u.c stuff
(mostly Spliterators).

As mentioned before, we will supply two explicitly concurrent Sets,
both via static factory methods:  ConcurrentHashMap.newKeySet, and
ConcurrentSkipListMap.newKeySet. (The CSLM one gives Sorted/Navigable Set)

These are necessary when people need/want parallel collect-into
operations for sets.

But how will they know to do this?

-Doug