This saves the order of clients in a property called AWESOME_CLIENT_ORDER on the
root window during shutdown. During startup, after managing all existing
windows, we force the client list into the order described by this property
(overwriting any changes that Lua possibly did).
This code should safely handle cases where the property doesn't contain all
existing clients or contains a client which doesn't exist anymore.
Signed-off-by: Uli Schlachter <psychon@znc.in>