Driver can connect to app on errors in on.initialize.

Driver can connect to app on errors in on.initialize (and `on.load_settings`).

  driver, define on.initialize with a run-time error:

  driver, define `on.initialize` with a run-time error:

  driver, define on.initialize with a run-time error:

  driver, define `on.initialize` with a run-time error:

Driver can connect to app on errors in `on.quit` (and `on.save_settings`).
* clone this repo to a new client app, clear its save dir, run it, run the
  driver, define `on.quit` with a run-time error:
    ```
    on.quit = function()
        foo = bar+1
    end
    ```
  Hit F4.
  Try to quit the client app. It shows an error and refuses to quit.
  Edit `on.quit` in the driver and remove the error:
    ```
    on.quit = function()
    end
    ```
  Hit F4. The error disappears from the app and driver.
  Try to quit the client app. Now the quit succeeds.
* clone this repo to a new client app, clear its save dir, run it, run the
  driver, define `on.quit` with a run-time error:
    ```
    on.quit = function()
        foo = bar+1
    end
    ```
  Hit F4.
  Try to quit the client app. It shows an error and refuses to quit.
  Hit F4 again in the driver (without fixing the error).
  Try to quit the client app again. It continues to show the error.