ecore: add ecore_event_type_flush.

ecore: add ecore_event_type_flush.

During shutdown it is possible that some event are still in ecore events
queue and get processed after the shutdown of the module that did emit them.
This would lead to crash in some case. The answer to this problem is to
normally manually track all ecore event in the queue and destroy them
before shutdown... Of course that make the API difficult to use and
basically nobody got it right.

This new API do actually as it says remove all the ecore event of a
certain type from ecore events queue. It is to be called on shutdown.

@fix