API Review: Missing UNSORTED Comparator constant in SortedList

[Martin Sladecek]

Hi,
while discussing the SortedList, we were talking about how to return to 
the unsorted state and the proposed solution was to have special 
SortedList.UNSORTED constant for comparator.

Unfortunately, I forgot to include it in the final proposal, so I'm 
proposing this now.

Thanks David Qiao for noticing this ( 
https://javafx-jira.kenai.com/browse/RT-30831).

Thanks,
-Martin