The commit history in github url looks about right. That's what I get for looking in launchpad's "mesa" project for a mir related branch. I didn't see an lp branch under mir corresponding to any mesa code and I completely missed the github url.
Hopefully this is enough to get a testable mir binary built outside of Ubuntu.
Though it would be reassuring if roaf blessed the github repo as matching mir tip in some ornate ceremonial ritual blessing...or just an update to the mir build from source instructions. But in the meantime... tallyho!