events,lib: don't require EE#listenerCount()

Now parts of our public and public-ish APIs fall back to old-style
listenerCount() if the emitter does not have a listenerCount function.

Fixes: https://github.com/nodejs/node/issues/2655
Refs: 8f58fb92

PR-URL: https://github.com/nodejs/node/pull/2661


Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>