Upstream 0.17.0 merge

@uganson or @TomDunham to review please.
This brings our fork up-to-date with upstream 0.17.0.

There may be some minor back-compat issues - related to keyword arguments. I've bumped into problems with require.python.virtualenv and require.files.*file, but they're trivial to fix. Those are all fixed on my DB replication branch on the platform, but I haven't looked at adtrack.