Since we've got lots of per-screen information spread across several arrays,
and for future features (eg. mult-upstream support) yet more to come, it's
time to consolidate into a per-screen private structure.
Initially just moving the upstream root window ID into it - others follwing
by subsequent patches. Leaving it as a global array and not assigning
private data to Screen structure yet.
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Enrico Weigelt, metux IT consult