Cast results of implementedEvents to an array.

This makes using mocks much easier with event listeners as they don't
need to provide a returnValue for implementedEvents.

Refs #2333
Update CakeEventManager.php

Cast resultados de implementedEvents a una matriz.

https://github.com/cakephp/cakephp/commit/e6f2c92005cfb5850159621da182f9b4f327fdd2
Merge pull request #2427 from EliuFlorez/patch-3

Cast implemented events to an array when detaching listeners.

This makes it much simpler to work with mocks, and avoids warnings caused by developer error.