Fix BranchHeads to work with branch2*

As of
http://selenic.com/pipermail/mercurial-devel/2013-November/054749.html
the new format should be:

<branch head hex node> <open/closed state> <branch name>

Ran into this problem on Mercurial 3.0.2.
Merge pull request #1 from Southern/fix_branchheads

Fix BranchHeads to work with branch2*