Bug#933959: xfce4-panel: Option to configure panel placement on external monitor only

[Pavel Reznicek <Pavel.Reznicek@cern.ch>]

Hi Yves-Alexis,

> I'm not sure I understand the use case here, can you be a little bit more
> specific?

Sure, sorry for not writing that clearly from the beginning. The use
case is when one often switches between a "laptop-only" mode
(typically at home) and a dual-display mode (at work, using both the
laptop screen and the external monitor). The panel should behave like
this:

- - when there is an external display, the panel should be shown on
the external display
- - when there is no external display plugged, the panel should not be
shown at all

I.e. the wish is to have panel that appears on any external monitor,
but never on the laptop screen.

Xfce4 has an "automatic" panel placement option, but that settings
shows the panel on the primary laptop screen when there is no external
display.

Moreover, in the recent past Xfce4 used to distinguish between how to
external monitor is connected (video ports on laptop, connection from
docking station). As a result, one would have to reconfigure the panel
every time a different connection to the external monitor was used.
The patch is written in a way it does not care how the external
monitor is connected/named, but simply put it on whenever there is
*any* external monitor present.

Best regards,
Pavel