When windows are set as "above", they will basically behave as "ontop"
(under normal circumstances) and therefore an indicator is useful to get
displayed in that case, too.
Closes https://github.com/awesomeWM/awesome/pull/325.
Currently `tasklist_update` gets triggered often, because it listens to
a lot of signals.
This patch makes it only call the last one through `timer.delayed_call`.
Daniel Hahler
Julian Wollrath