(copied from email reply) "Sorry! I thought you would be notified, but I guess the discussion was all on the list rather than in an Issue.
It was pull request #621, merged June 10. You can see the code changes at: https://github.com/JuliaStats/DataFrames.jl/commit/3cf97fffde38517783d41f431da12714766a51c9 " A 2nd pull request relaxed the typing on the Associative argument: https://github.com/JuliaStats/DataFrames.jl/commit/d5f657d6be4df63a76e61fbaa4f43c8a54df3132
