RFR(m): 8139233u1 add initial compact immutable collection implementations

[Stuart Marks]

On 5/6/16 10:57 AM, Stuart Marks wrote:
> I've been doing too much last-minute refactoring.

Actually that's wasn't the cause of this bug. The bug was in the previous webrev 
and also in the prototype from my branch in the sandbox, so it's been in there 
quite a while.

Again, thanks for spotting it.

s'marks