Change history shows multiple heads in hg repo, without indicating which branches the revision is head of

When you look at the history of a file in an hg repo (and possibly other types – haven't tested others) you see multiple revisions marked HEAD, all of which can be shown as committed to the default branch. This is because some of them are the HEADs of branches, but no commits have been made to that file on the branch since the branch was created.

We need to make it easy to see which branch the revision is head of – perhaps by putting a branch name next to the HEAD icon?