Various merge corrections

I've diff'd this patch against my own -- since they were both created
independently, this means that two sets of eyes have gone over all the
merge conflicts that were created, so I'm feeling significantly more
confident in the resulting PR.

@rxin has looked at the changes to the repl and is resoundingly
confident that they are correct.
Use Kafka 2.10 (again)
Merge pull request #1 from aarondav/scala210-master

Various merge corrections