#2408 Addons overwrite aircraft-set.xml

Addon addon-config.xml overwrites properties set by aircraft-set.xml.

As addons are meant to be as "fgdata mods, but without having to edit fgdata directly", should they instead go on top of fgdata's properties and let aircraft write its own properties after?

Example: the HUD provided by addon
https://gitlab.com/mdanil/flightgear-mickey
overwrites version of the same HUD that is included with the aircraft and adapted to its controls:
https://gitlab.com/mdanil/Tu-144

[James Turner]

This is unfdortunately the way the ordering has to work: it's very difficult to load anything before the aircraft -set.xml, but anything we load after can of course overwrite its properties.

The add-on design, relies on the author of the add-on to be careful about such situations, I think.

[Anonymous]

They also overwrite --prop:, but inconsistently: if it's in launcher's additional settings, they overwrite, but without launcher, --prop: in fgfsrc work just fine. Iirc this hasn't always been the case, it used to work in launcher.

[James Turner]

Apparently we can actaulyl change this: my planis to make the change on next, test it, and then back port to the LTS.

The launcher --prop being overwrriten might be something different, we will need to check it.