User: use a stably-ordered queue for long-polling #234
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If the AJAX request for LongPollServlet happens with enough of a delay,
there may be two stateful messages in the queue -- I have observed two
GAME_STATE_CHANGE messages enqueued simultaneously when the Card Czar
does not long-poll while the other players progress the game through
PLAYING to JUDGING. The JS code overwrites the state as it iterates the
list, so the "last state wins". But PriorityQueue explicitly does
not guarantee any particular ordering among elements that compare
"equal", causing the client to think the game is PLAYING.
Testing done
This avoids one flavor of error in a local client I'm developing, but to be honest, I'm still not finished debugging all of the other state-machine issues that it had.