Currently, the working directory's status is on the same button as the branch name. This was fine, but the expected action is different for the two:

* clicking the 'status' button should show the differences ('thg vdiff' or 'fossil gdiff') when there are any, or just launch 'thg log' or 'fossil ui' when the workdir is clear.
* clicking the 'branches' button should just show the drop-downlist of branches, and allow updating to a different branch