There was some discussion in IRC of how to test out the new unit refactor branch. Not all of the frontends have been converted.
Here's how to pull it:
hg pull -r unitrefactor http://bitbucket.org/MatthewTurk/yt hg up -r unitrefactor
Then, build as usual. As a reminder, this is the primary yt repository now:
If you have that set as your "default", you can get back to the tip of that repository like so:
hg up -r "remote(tip)"
If you want to make sure you're updating to a specific branch, swap out "tip" for "yt" or "yt-3.0" (which will need to be in quotes, as - is a special character in revsets.