[util/popup] fix endless loop on "close on leave"

When closing a popup window when the mouse leave the area (default
behaviour, unfortunately), the main "show()" got stuck in an infinite
loop.

Fix that by setting running to False when exiting.

fixes #844

bumblebee_status/util/popup.py

@@ -49,6 +49,7 @@ class menu(object):
         return self._menu
 
     def __on_focus_out(self, event=None):
+        self.running = False
         self._root.destroy()
 
     def __on_click(self, callback):