Optimize EventRule
Optimize EventRule

- provide anumber of opportunities to exit early
- determine whether we're adding or removing an event instead of checking
  every single event to see whether it's an adder or remover

FakeItEasy/FakeItEasy,blairconrad/FakeItEasy,thomaslevesque/FakeItEasy,thomaslevesque/FakeItEasy,FakeItEasy/FakeItEasy,adamralph/FakeItEasy,adamralph/FakeItEasy,blairconrad/FakeItEasy