Comment 4 for bug 1197727

You choose which version you want by clicking anywhere on the pane showing that version. Which version is selected is shown by the border around it. It's simpler and more direct than having controls separate from the panes, though I guess it would require a bit of cleverness to make the panes selectable that way.

I wonder if you could use "wdiff --no-inserted" for the left pane, and "wdiff --no-deleted" for the right pane, using "--start-delete" etc to insert the Pango formatting commands for coloring the background of the changes.