Allow infinite ActiveState change listeners.

Fixes a warning from event-emitter when using more than ten Links (or
other components using the ActiveState mixin) by allowing an unlimited number of listeners (as suggested here: http://nodejs.org/docs/latest/api/events.html#events_emitter_setmaxlisteners_n). 

This is to try to fix issue #220.

Or would it be better to somehow group event listeners? Or is there some other way of solving this problem?

(Sorry if I'm doing this wrong, haven't done a pull request before.)