Comment 29 for bug 1605937

hrm... wingpanel has a dbus plugin that should interact with Gala to handle focus, but i'm not sure that it works. either way, it's not good that wingpanel steals/keeps focus inappropriately in the first place.

This SO answer shows a way (in python) to get the previously focused window at focus-in-event:
http://stackoverflow.com/a/36137157

Maybe there's a way to use this to get wingpanel to revert focus when indicator popovers close, without relying on dbus and gala.