async.queue emits "saturated" event at wrong point

[glenjamin]

In the https://github.com/caolan/async#queue docs it says:

saturated - a callback that is called when the queue length hits the concurrency limit, and further tasks will be queued.

This is both correct & incorrect.

A queue has both a number of running() functions, and a queue of functions to run length(). The event is emitted when .length() === concurrency - whereas it should really be emitted when running() === concurrency.

Example:

var q = async.queue(function(){}, 2);
q.saturated = console.log.bind(console, "full");
q.push(1);
q.push(2);
// would expect "full" here
q.push(3);
q.push(4);
// but actually get "full" here

[aearly]

You are correct, this is misleading. I fixed this as a side effect of other changes in #704