Fixed an issue with notifications and recursive promises

[chrisdp]

The code supplied here results in only the "outer" being called:

recursivePromise = promises.resolve(true)

promises.onFinally(recursivePromise, sub(recursivePromise as dynamic)
	print "outer"
	promises.onThen(recursivePromise, sub(recursivePromise as dynamic)
		print "inner"
	end sub)
end sub, recursivePromise)

This PR addresses a case where registering listeners from within a callback on the same promise fails to correctly notify all the listeners.