e3dd2b1591
This is a more complex approach, which makes me really want to use IDProperty instead (assuming we handle their merging nicely). In fact I would expect this to happen in readfile.c, not during doversion, but I can revert this later. For now this allow for demo files saved with 2.8 to keep working even after we add/remove engine settings properties. The values are merged. There is no purge though, so old CollectionEngineSettings and CollectionEngineProperty will live forever (for the time being).