@dhermes this has a conflict too. Otherwise LGTM.

@daspecster I just rebased and it seemed to fix itself?

Build time down from 20 minutes to about 7.5 minutes. But it used to be consistently under 4, so I still have work to do.

I don't see any special handling for changes in core/ -- because it is a dependency for everything else, should we be falling back to running all tests when any change happens there?

@tseaver I've got a change coming down the pipe which computes a package dependency graph and then follows the tree to populate a more-full list of changes. Thanks for being heads up!