eo/eina: Add HACK to avoid calls to EO after shutdown

eo/eina: Add HACK to avoid calls to EO after shutdown

Efl.Future is an EO object which means even cancelling Efl.Future
objects requires EO. So this should be done before shutting down EO,
otherwise everything fails badly.

I believe Efl.Future is going to disappear soon, but the problem will
remain: if any promise/future uses EO or anything else outside of Eina
(so, basically anything) then it needs to be canceled before shutting
down the above layers. This is the same situation as with ecore events,
for which we've introduced ecore_event_type_flush.

Ping @cedric