list literal gotcha and suggestion

[Florian Weimer]

* Gene Ray:

> "Rare"?
>
> In my experience, Sets are not rare in well-written code; they're
> only rare in code where for whatever reason the developer has
> refused to use them, and instead expends effort and CPU time
> iterating through an array or ArrayList to achieve the equivalent
> functionality.  Encouraging this sort of behavior further by
> including only Lists in the new syntax is not a good plan.

At least in JDK 6, the HashSet and TreeSet are wrappers around the
corresponding maps.  If there were more users, there would be a
compelling reason to reimplement them without superfluous value
references. 8-)