ENH: Smaller test dataset (320MB)

We'll see if Travis can actually run this. I have a bad feeling that, with all the additional tests that will be run, we will exceed the ~50-minute limit.
@agramfort are you okay with this? I'm not sure if the commands should be covered or not. If they should be, we should probably write some tests for them using `run_subprocess`, which I could do as part of this PR or a subsequent one.