compositingActive not efficient on XRandR events

[Alex Fiestas]

Hi there

One of the issues I have when I setup my XRandR config is that plasma 
fails to set the composite theme (the good looking with ARGB one).

After thinking about it a little bit, and knowing how KWin and Plasma 
are handling XRandR events I think I know where the bug is.

When adding a new screen XRandR produces 3 events: move, resize, 
screenAdded. For each of these events KWin will restart the composite.
At the same time, Plasma listens ot each of these events and do its part 
of the job (resizing panels etc), and I guess that is in these events 
where plasma updates the Theme (and ask if composite is on). This will 
eventually fail since KWin can be in the mdidle of restarting the 
composite, so Plasma will sue the not-compositing theme instead.

After checking how KWindowSystem::compositingActive works on X11 I'm out 
of ideas of how to fix this issue correctly, so maybe we've to add a 
workaround in Plasma or maybe something else between KWin and Plasma.

Any ideas?

Thanks.