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Ok, I think it's all set. Tested it with the challenge you provided, dropped it into my currently running melee test a half hour ago and that still looks right, and did my usual round of manual setup and tests. The fix was mostly pretty easy thanks to Guava's Multimap stuff, but it also led to some minor refactoring so that nothing is based on looking up a score only by bot name, besides the challenger bot. I think it should work fine even if the challenger is also a reference bot, even though that seems silly - the first score for that bot in each battle would be considered the challenger score.

Hopefully it won't be too painful of a merge for you. ;)