setPreloadMessage

[d.healey]

I'm reworking my zip extracting script and trying to decouple it from my progress bar script. And I just realised (or possibly re-realised) that it uses the same preloading thread as samples. So I can just monitor it from a panel's preloading callback.

However I also want to display a nice message based on the preloading state (number of archives extracted).

Again to stay decoupled I thought I'd use the Engine.getPreloadMessage() but there is no way to set it to a custom value so it just says "Kill voices..."

So I've added a new function Engine.setPreloadMessage although perhaps some kind of unzip broadcaster would be a more suitable option in the future.