redefine events from within an event call

[da-h]

Remove the necessity to call
del event.myevent
to clear the cache.

In other words, any call to
mf.register_event (within an event?) should to this by itself.

I think it would even be better, if any call to mf.register_event would do that.

Note: Think also about a nicer way to pass the module's mf-object from the registration phase into an event.