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Emits an event on an EventEmitter where the listener may include a callback function

An asyncEmit() function that accepts an EventEmitter, an Array of args, and a callback function. If the emitter listener function has an arity > args.length then there is an assumed callback function on the emitter, which means that it is doing some async work. We have to wait for the callbacks for any async listener functions.

It works like this:

var emitter = new EventEmitter()
// this is an async listener 
emitter.on('something', function (val, done) {
  // val may be any number of input arguments 
  setTimeout(function () {
  }, 1000)
// this is a sync listener, no callback function 
emitter.on('something', function (val) {
asyncEmit(emitter, 'something', [ 5 ], function (err) {
  if (err) throw err